[In Cabin in the Woods] the reference is to a creepypasta, a rather old one, called the "Russian Sleep Experiment". Now, in the story... they locked a bunch of Russians in a room for 15(?) days deprived of sleep using some kind of gas, they all went crazy and ate each other within 15 days, except 4. In the movie there is a scene where it shows 4 (I believe) men in labcoats eating some corpses in a room. But, what really struck me is the similarity to the picture I saw attached with the creepypasta (I couldn't find it, it's been so long. It was a drawing, anyway).
It's an interesting point. Watch the scene where the monsters escape from HQ and see if you can spot anything resembling Russian Sleep Experiment patients!
I think that this is probably the moment the OP is referring to — men in what seem to be hospital gowns descending on a victim.
There are another couple of moments that could fit the bill, including the chompers in the bottom right of the gore chamber (although these look very much like classic Romero zombies).
In another scene, when the camera pans over a number of small screens there's *something* feasting on a carcass.
The most famous image from the Russian Sleep Experiment story is this one (below) and I couldn't see anything resembling this closely.