AdrynBliss

The key to any trick is misdirection. Remember how he specifically tells Watson to 'stand right there' and then he's hit by the cyclist. I believe there was a similer trick pulled in a ep of CSI, i think. A previous poster pointed out the ground had been marked, the patch of ground replaced by a softer substance, obviously and in the few moments John is distracted a lid or cover placed over the top (most likely by his version of the irregulars, the homeless network) and of course the whole post mortum aspect, well, it's handy having a pathologist as a friend. edit: also if i had to make a guess the soft material he landed on would be a rubber sheet over a hole, ergo the bouncy rubber ball.