This is something I’ve noticed with Tom and Frank: Rabbits grind their teeth in pleasure (a.k.a. purr) at two speeds. The slow speed is about 208 beats per minute (check this online metronome!), and comes most often in groupings of three, but also sometimes in twos or fours or, less commonly, singles or quads. The fast speed is, as you might expect, faster — too fast to count, and it generally lasts around two to four seconds at a time.