Lizard corpses should go tainted like any other corpse, though they will still never rot away completely.

Occasionally when suffering from food poisoning, you vomit, which will then save you from dying (but still remove a lot of nutrition which means you’re probably still in some peril).

The amulet versus poison (and only this) prevents food poisoning from tainted corpses.

Some monsters’ corpses, like rats, have a chance of conferring FoodPois when eaten, regardless of whether they are tainted.