Literally swapping bodies

Jon glanced around, but didn't notice anything happening. With a shrug, he got out his iPad and started browsing his favourite sites. Jon had a secret fondness for head swaps, where someone took a head from one photo and pasted it onto the body of another. He especially like the ones where male heads were put on female bodies and vice versa. Before long it was dark and he decided to turn in for the night. As he drifted off into sleep his mind wandered into thinking about head swaps. He started to imagine the heads belonging to people he knew and grinned at the thought of Sarah's head on the body of a forty year old fat slob or Biff and the football team's heads being on the bodies of little girls. Bizarrely, he started thinking of his own head being swapped too, one body in particular coming to mind. Unnoticed by him, as he dreamed he began to change. And so too did everyone else. Come morning, the whole town would find that they'd been swapped.