When Reddit user Katzmatt shone a UV light on his jar of peanut butter, he noticed something a bit unusual: It glowed in the dark (just like urine).

Is the jar of peanut butter contaminated? Did someone piss in his jar? Or does peanut butter just naturally glow-in-the-dark?Katzmatt was intent on solving this mystery.

He tested other food items in his house and compared it with the jar of peanut butter.

These are the items that glowed:

peanut butter (brightest and longest lasting)

peanuts (dim but lasting)

almonds (dimmer and short lived)

cashews (bright but very fast)

pine nuts (almost unnoticeable)

sesame seeds (very dim and fast)

These are the items didn’t glow:

walnuts

peanut oil

olive oil

sesame oil

coconut oil

coconuts

brazil nuts

What’s the deal with deez nuts? (I just had to go there.)

As user PlatierZoysias points out, several types of nuts probably glow because of delayed luminance, which is a really trippy and fascinating phenomenon that occurs in nature.

Interestingly, lots of plants and animals emit a very faint glow when under a UV light, according to a paper cited by the user. The glow usually lasts for a few seconds before fading.

Reddit user KatzMatt

But this still doesn’t explain why peanut butter glowed the brightest.

It turns out, peanuts contain phenolic acids. I know what you’re thinking: This sounds like a scary word. But phenolic acids are actually a really good thing. This stuff can help prevent heart disease and other nasty ailments.

Roasted peanuts contain a lot more phenolic compounds than raw peanuts, according to a University of Florida study. And peanut skin, in particular, is loaded with phenolic acids.

And guess what peanut butter is usually made-up of? Roasted peanuts and ground peanut skin.

Okay so you may be wondering why phenolic acids are so important to this story.

Apparently, phenolic acids fluoresce in a blue-green color spectrum under a UV light.

It’s possible that peanut butter’s glow is a result of all those extra phenol compounds, but we won’t know for sure without doing a more in-depth experiment.

In any case, phenol compounds sound like an acid-lover’s dream.