system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] What exactly is a mushroom? How do they differ from plants or animals? And what makes some safe for human consumption?
gpt
A mushroom is the fruiting body of some types of fungus. The reason the fungus living in the soil underground or in a rotting log grows them is to distribute spores which are like mushroom versions of seeds.

Fungus are an entirely separate branch of life from plants and animals.

Some of them develop a poison which can kill people who eat them. Some don't.  Producing a poison takes extra energy, so ones that don't probably developed in areas where there were less animals likely to eat them.