Typically pack (or school) hunters, piranhas can famously eat wading cows, which are notoriously slower than field cows, in under five minutes. Fresh water lovers, but eminently adaptable, piranhas are often found outside of their natural waters by people humorously restocking various water sources. The most prominent example of this is perhaps the case of the girlfriend who, angry with her boyfriend for forgetting her birthday, bought ten of the fish. She then cut a hole in the mattress of his waterbed and inserted the fish, then taped over the hole. Her boyfriend was unaware of his new pets until they chewed through the plastic and into his rear.

They are not suitable for use as domestic pets, and in fact are partial to consuming most domestic pets, especially those most guilty of curiosity, like cats or budgies.