Phytohemagglutinin is a toxic agent found in many beans, but in highest concentration in red kidney beans.
Consumption of phytohemagglutinin, through as few as 4 or 5 insufficiently cooked kidney beans, can cause nausea, vomiting, diarrhea, and severe abdominal pain. Symptoms usually dissipate on their own after three to four hours.
Phytohemagglutinin is a glycoprotein, lectin, which requires a sufficiently high temperature to be inactivated. Slow cookers, and simmering at low temperatures, can increase the potency of the toxin. Soaking for a minimum of five hours and boiling for a minimum of ten minutes, with some agencies recommending thirty.
Raw or insufficiently cooked: red kidney beans, white kidney beans, broad beans
U.S. Food and Drug Administration
Kidney bean lectin