toxoplasma is a brain parasite that ultimately wants to end up in a cat’s gut.
to do this, it re-wires rat brains to make them reckless and unafraid. the parasites sometimes inadvertently end up in human brains. infected people are inclined to be oblivious of other people’s opinions of them and to disregard the rules.
we’re not exactly sure what causes us to do the things we do, but for now “brain parasites” is the best excuse.