What happens to Peter the cat?

Peter the cat goes a bit crazy after Tom doses him with Aunt Polly's pain killer.

Peter was agreeable. So Tom pried his mouth open and poured down the Pain-killer. Peter sprang a couple of yards in the air, and then delivered a war-whoop and set off round and round the room, banging against furniture, upsetting flower-pots, and making general havoc. Next he rose on his hind feet and pranced around, in a frenzy of enjoyment, with his head over his shoulder and his voice proclaiming his unappeasable happiness. Then he went tearing around the house again spreading chaos and destruction in his path. Aunt Polly entered in time to see him throw a few double summersets, deliver a final mighty hurrah, and sail through the open window, carrying the rest of the flower-pots with him.