Unhealthy Rotten Flesh
Rotten flesh is not a food, but it can be eaten, so it causes bad effects when eaten.
The eating of rotten flesh causes a type of damage to the consumer called flesh poisoning, and also short-term poison and nausea effects.
At this time, flesh poisoning only causes half a heart of damage, and the related death message mentions "cannibalism".
With all of these effects combined, rotten flesh is no longer useful for sustaining a character, as a food.