Not exactly bizarre, but it’s fun to learn that the delicious fragrance of shrimps and crabs when cooked comes from chitin, and chitin is also why sautéed mushrooms smell/taste like shrimps.

And since fungi are mostly chitin, plants have evolved defenses against fungi by producing enzymes that destroy chitin, which is how some plants eventually evolved the ability to digest insects.

EDIT: a previous version of this post mistakenly confused chitin with keratin (which our fingernails are made of). Thanks to sndrtj for the correction!