Why bother keeping them in a box they can move around in? Just crush them and keep it that way. I understand that there could be more, but you can just plop them in with the water refill. That or you could just submerge them in concrete. The effects are very similar to 871. I think the article is still great, this is just a warning about how this'll get compared to it. "Addendum XXXX-03" is oddly similar to too spooky, but your skip is immediately recognizable as dangerous, so it doesn't really need to be there.

Now onto the nitty-gritty.

I'm going to miss some stuff.

Comments made as I go.

SCP-XXXX refers to a species

I feel like this would be better as "SCP-XXXX is a sentient humanoid species"

Subject's necks appear 'twisted' or dislocated in places, presumably due to the nature of SCP-XXXX's reproductive cycle.

Don't use quotation marks for effect, twisted is correct. I'm about 70% sure "Subject's" is an incorrect use of an apostrophe. I feel like this would be better as "necks are dislocated and are capable of twisting X°." The reader can infer that this is caused by the birthing process.

Blood samples show high acidity levels (pH 2) and are comparable to the strength of molar three hydrochloric acid.

I understand that this justifies a part of the containment procedures, but what purpose does it serve the article?

a ‘red zone’ radius

I think you can drop 'red zone'.

acts as a form of insulation, accelerating hatch rate.

So it's a pseudo-placenta? Because that's (mainly) what a placenta does.

⦁ Extreme blunt-force trauma.

⦁ Pressures exceeding 180,000 psi.

Blunt-force trauma and raw pressure are pretty much the same thing. It could probably be condensed into one, or you could specify how long it was exposed to the psi for.

their internal organs having been [DATA EXPUNGED] and heavily ruptured.

Is this an inconsistency with the liquefaction bit in the description proper or is this intentional?

three mile radius

Accidental use of imperial here.

several years- but' never caught

I'm pretty sure you should use quotation marks here. The apostrophe isn't put in the right place.

Approximately thirteen chicken carcasses, with precise incisions located on the underbelly, neck and thigh.

How is it approximate? Were the chickens completely obliterated, except the underbellies, necks, and thighs? I'd recommend using the Oxford comma.

Paste is a deep brown in colour

Minor typo; it should be "Paste is deep brown in colour"

(sic)

sic is normally used to denote typos being presented as they originally were written, so it doesn't belong here.

Perhaps we have more than one SCP object on our hands.

I don't see why. Since the XXXX-03 says it creates eggs at a rapid rate in open areas, an absolute max of 110.77 86,400 eggs can be made per day, per individual chickman (Assuming one egg laid per second). Despite wikipedia, I'm not sure how to calculate this, but the chickmen would probably be in the billions by nightfall/the end of the week, meaning it's a miracle the Foundation could contain them before a fourth was made.

SCP-XXXX considers the liquid around is as 'full space'

Wouldn't it then consider being buried underground as full space?

The former theory holds more water

Goddamnit, I see what you did there.

Dr. Ewing: You're under no obligation to look.

Look at what? The picture? It's not very clear what you're saying here.

they were. Kids.

I feel an ellipsis/comma would be better for the flow. Currently, it reads awkwardly.

20°F

Another use of imperial. 7°C should be the right conversion, but I might be wrong.

-310°F

-190°C.

This was to be expected, after visible cracks began surfacing on its shell approximately 30 minutes into liquid nitrogen exposure.

This doesn't seem clinical. You could state that cracks appeared 30 minutes into the bath before saying they were shattered.

Throwback to:

Its eggs are potentially indestructible

Because in Experiment B, it's found that you can destroy them, which makes me wonder why

The Foundation is keeping four of these things instead of one. Why they bothered to leave Addendum 03 up.

Second throwback to:

Composition of shells are as of yet unknown

Because in Experiment B you state that the shards could be ground up, so chemical analysis should therefore be possible.

Otherwise, it's pretty damn good. I especially like how you let the skip have a way to properly and thoroughly get rid of it. PM me when you post it, because it's a definite +1 for me.