Were animals either escape or attack when we humans try to eat them, plants often produce toxic chemicals as defense mechanism. For some animals, eating something like a bean or cacao, can be deadly, whereas other animals can eat them without problems. (Lectins from beans are also not good for humans.)
For some people, citrus fruits can cause phytophotodermatitis:
An elinimation diet (like FODMAP or carnivore) could help finding these foods. Here’s also some info about it: Could it be diet related? - #4 by Tso
