Raw kidney beans contain phytohaemagglutinin, a toxin that can cause severe vomiting and stomach cramps. Eating just a handful of undercooked beans can lead to food poisoning.
Boiling kidney beans for at least 10 minutes destroys the toxin, making them safe to eat. However, cooking at low temperatures can make them even more toxic instead of neutralizing the poison so be extra careful when you’re slow simmering your chili.