There are five faculties (indriya): those of pleasure (sukhindriyaṃ), pain (dukkhindriyaṃ), happiness (somanassindriyaṃ), sorrow (domanassindriyaṃ) and indifference (upekkhindriyaṃ).
Just as from the rubbing together of two sticks warmth and heat are produced, so, from their separation, warmth and heat, thus born, are quenched; similarly from contact, experienced as agreeable, arises the faculty of pleasure, etc. S.v.211‑13.