(Theory) Sans ‘bleeds’ ketchup from a bottle, and why Sans has a monster soul and a monster body.

There are four popular explanations for why and what Sans bleeds when he dies. It’s either blood, ketchup from within his body (because he drinks so much), ketchup from a bottle hidden in his jacket, or determination.



TL;DR: Since Sans has neither a human soul nor a human body we can say it’s not blood. It’s impossible to be the ketchup that Sans drinks due to how monster food actually works in game. Determination is possible I guess, but since ketchup from a bottle has the most solid evidence out of all the options, I go with that.







Full reasoning under the readmore.

Let’s look at blood first. In order for it to be blood, Sans would have to be human or formerly human. There’s a problem with this because the game shows Sans as having a regular monster soul (no human soul) and a regular monster body.



Evidence for a regular monster soul can be found in the pacifist ending.



Flowey: “…all of your friend’s souls are gonna be mine, too!”

“The lost souls stand there.” (Souls. Papyrus and Sans in this case.)

“You feel your friends’ souls resonating within Asriel!”

Frisk can feel their friends’ souls resonating. Asriel should be able to tell a monster soul from a human soul. Neither of them acknowledge anything different with Sans’ soul; he is simply treated like any other monster.



Considering how powerful and important a human soul has been throughout the game, the fact that one would go unnoticed or ignored by those who should be able to tell that there’s an extra one hanging around is a bit of a stretch. It’s also not seen when Asriel shatters the barrier.

Perhaps Sans doesn’t have a soul. What if he’s a being of pure determination, like Flowey? It’s acknowledged in the game that Sans has a soul by the mere fact that he was able to become a lost soul. Flowey wouldn’t be able to take his soul if he didn’t have one.

If he doesn’t have a human soul, could Sans have a monster soul in a full fledged human body? There are a lot of reasons someone could argue that Sans has a human body, but I don’t think they check out.



He’s not wearing a mask. I know his smile doesn’t move (much) but his eyes certainly do. His eyes themselves are pinpricks of light. Human eyes looking out of a mask don’t do that.

When you hit him in the genocide run you do a great deal of damage, consistent with how monsters react to humans with a great deal of malicious intent.

Knowing about the sun and what humans look like doesn’t mean there’s anything out of the ordinary with him. Alphys, Undyne and that mouse wearing the big scarf in Snowdin all know about the sun, and Tsundere Plane is one of many monsters who can recognize a human.

He doesn’t consider the surface as it is now to be his home, the place that he gave up on trying to go back to, as per his comments during the genocide fight.

He has magic and the same types of attack as Papyrus.



Monsters are referred to as people multiple times throughout the game, so Sans’ photos in his lab probably aren’t actually referring to humans.

Sans sleeping while Papyrus doesn’t seem to need to (which in the game itself is contradictory) doesn’t mean that Sans is abnormal for a monster skeleton. I actually would argue that if anything Papyrus is the odd one out for not sleeping, if in fact that’s a thing he does. Monsters need sleep.

Sans’ ’breathing’ animation during his fight and Papyrus’ lack of one doesn’t mean that Sans is human. Papyrus also breaths, in a sense. He gasps, huffs, and puffs, and after all, Toriel doesn’t move during her fight either, but we aren’t going to argue about her lack of breathing ability.

For however much it matters, you can see his leg bones in his official Steam art. This artwork is fan made, but it was also given the approval by Toby.



Sans’ mouth moves and juice leaks out of him in the Kickstarter video. Now I’m not going to really cite this as a reason he’s not human since things could have changed since then, but it shows that Sans was never originally intended to be human.

Is the red leaking out of Sans bone marrow? Sans is a monster who has no brain, guts, or veins, to name a few, so why would a magic, skeleton monster have bone marrow? There’s no reason to have it, especially since its purpose is completely redundant. If it was bone marrow and if it was natural for a skeleton monster to have it, then Papyrus should have bled some as well.



If Sans doesn’t have a full human body, could he still be a human skeleton powered by determination and bleed bone marrow? A skeleton from a dead human won’t be producing further bone marrow, and I think it’d a bit far fetched to say that determination would resume that particular job. Bone marrow should have long since dried up, and there wouldn’t be enough of it to drip down from Sans’ mouth if it hadn’t.



In any case, Sans would be in the same scenario as Flowey. They are something dead/inanimate and given the will to live. This does not give Flowey a soul, and he has a rather tortured existence because of it. Sans also should not have a soul, but he does. The game states that souls cannot be made artificially, so the idea that Sans was somehow given a soul through Gaster and experimentation is impossible.



The very notion that giving a soul to a creature awakened from determination is possible in the game makes Flowey’s entire painful existence and self-confinement to the Underground post game a far more cruel an idea than it already is. It would even make Alphys’ work on determination redundant if souls could be created.

The game’s plot hinges on the fact that souls cannot be created artificially, and so I don’t think Sans could be the remains of one of the fallen children. There’s no room in the game’s lore to give him a soul.

If what Sans bleeds isn’t blood, then next popular option is ketchup because Sans guzzles the stuff and it leaked out of his body when you hit him. Sans’ habit of drinking an excessive amount of ketchup is just a fan interpretation of the scene in Grillby’s. Sans only drinks it once in response to a failed prank, and other than that there is no mention of Sans drinking ketchup in the game, or even being unusually fond of it in general. Regardless of what your headcanon is, in the logic of the game this is impossible anyway.

Big Mouth: “To a human, monster food would be very interesting. As soon as you eat it, it converts perfectly into energy.”

This comes from Big Mouth in Grillbys. As soon as Sans drinks it, it ceases to be ketchup. Sans can’t bleed something that no longer exists in that state.

One other theory is determination. I used to believe this was the case, but have lately changed my mind.

Undyne: “Deep, deep in my soul. There’s a burning feeling I can’t describe. A burning feeling that WON’T let me die.”

Undyne just described determination as something that exists in her soul. Determination also exists in a human soul, as those are what Alphys uses to extract the determination from for her experiments. Determination is in the soul, not the body. If Sans does has determination, there’s some reason to believe that it isn’t something that would be capable of being bled out.



Where does Flowey keeps his determination since he has no soul? No idea; perhaps determination in any form becomes a form of energy, and as such can’t be bled. Flowey certainly never bleeds when you kill him, and the Amalgamates never bleed either. All of these characters are chock-full of determination, more than Sans would be.



Sans not bleeding determination wouldn’t mean that he couldn’t have determination at all; it simply means that artificial determination is not something that can be bled out of the body. Natural determination definitely can’t be bled from the body, because otherwise the DT Extractor isn’t needed.



But the real reason I switched from believing that the ‘blood’ was determination is because a bottle of ketchup has some in game evidence.

1. We know that Sans does actually keep a bottle of ketchup in his jacket somewhere, since he pulls it out at Grillbys, and prior to that there was no ketchup in sight. This doesn’t mean that he carries it around for a snack, but it serves the same function as his whoopee cushion; for pranks. He pranks you in Grillbys and pranks you again at the end.

2. The colour of the ‘blood’ may also be important.



As we can see, there is really no set rule to the colours and what they mean, as we can see how Alphys’ blushing in the credits is different than when when she actually tips over. Just because something is the same colour doesn’t necessarily mean there’s a direct link between the two. Even so, that doesn’t mean that there can’t be a link between some instances where Toby has used the same shade of red.



While #ed1c24 may not be reserved for ketchup and vegetables specifically, I still think there’s a good chance a link between the two was intentional.



3. And lastly, this tweet by Toby, which I think hints at the truth, rather than purely being a joke. https://twitter.com/fwugradiation/status/660542883360079872

EDIT: Toby has since deleted that tweet (like he has with many lately), and since I can’t find direct evidence of it, you’ll have to take my word for it. https://twitter.com/Slinktress/status/661319877077147648 This was the original tweet, where Toby replied with “ketchup filling.” The comment in the link there, “the game truth is in the Undertale cookies!” may be the only thing left (that I can find) referencing Toby’s tweet.



How does ketchup leak out of his mouth then if it’s just from a broken bottle? Well, it shouldn’t. Bleeding from the mouth is commonly meant to show internal injury, and besides that, there’s no real way Sans should be leaking ketchup from his mouth if the bottle was slashed. I think Toby isn’t concerned with whether or not this should actually be possible, but more concerned with how the scene will function visually and how to sell the red we see on Sans as blood even when it isn’t.



There are some things in the game that we should hold to a standard, if they are possible within the game’s lore and with what we know of reality. Then there are other things that don’t need to be questioned and are simply a result of video game logic, where the intent and visuals are more important than the ‘how’. Undertale is a game, one that is very lighthearted at times. But to try to support or disprove something based on real world physics can be rather shaky, since the game itself defies these on a regular basis. For everyone this point is at different places, and that’s perfectly fine. I know that I’ve probably taken things more literally than they were meant to before, and possibly already done so to some people further up in this very post.



But for me personally, the exact reasoning of how the ketchup leaks in the body of a skeleton doesn’t need to be explained or looked at in detail, just like how Papyrus’ ability to blush doesn’t need to be questioned. What’s important is that we know that Papyrus is feeling bashful, and in Sans’ case here it’s to give shock and confusion for the viewer. Ketchup leaks from his mouth because it’s meant to give the initial impression that Sans is in fact actually bleeding, which is needed because this is yet another prank from Sans, to trick us into thinking one way when the answer lies in a different direction.



So as underwhelming as ketchup is to something like determination or blood bleeding out, it fits in line with what we know about Sans. He pranks us numerous times throughout the game, and this is simply his final prank.

