| When you cuddle a cat for an extended period of time, and he is purring loudly, you can stop cuddling him and he will continue to purr for a short amount of time afterwards. This is known as purr inertia.
The amount of time the cat continues to purr is directly proportional to the amount of time you were cuddling him, T, and his contentness level, C, by the following equation:
(T * C) * 10 = P
P is in seconds. The amount of time is also dependant on how comfortable the cat is. YMMV. | 
