If you put a piece of pineapple somewhere in your mouth it starts ‘eating you’. It has proteins that degrades meat.
Pineapple contains bromelain, a mixture of two protein-digesting enzymes (called proteases), a corrosive chemical that breaks down amino acids (that’s why pineapple is an effective and delicious meat tenderizer). When you eat pineapple, bromelain does this same protein degradation on your mouth.