PAIN-TASTE OVERLAP. “Another “non-taste” taste is the burning of capsaicin, the molecule that gives hot peppers their kick. Capsaicin binds to a receptor on cells that detect temperature and cells that send messages of pain. The same receptor and related ones are activated by piperine, a compound in black pepper that you might shake on your eggs in the morning, and allyl isothiocynanate, the burning compound in mustard and radishes.”
http://www.bbc.com/future/story/20150120-hidden-ways-your-tongue-tastes