The last magic trick

A magician is entertaining a childrens party, at the end of his show little Peter comes up to the magician tugs on his trousers and shouts
"Mr Magician, Mr Magician please do another trick!", to which the magician replies packing his stuff away
"Sorry, that's it, the shows over, no more magic tricks for today I'm afraid".
Still the little Peter persists...
"Mr Magician, Mr Magician, please do another trick!!"
To which the Magician responds again....
"No! no more magic tricks! now go and play in the garden"
Again little Peter persists "But Mr Magician, just one more trick!".
Annoyed, the magician gives in..
"Ok, Ok, just one more trick then that's it...".
Little Peter delighted with a smile on his face anticipates the magicians last trick....
"Bend over..." says the magician
Little Peter bends over
"Now................ can you feel my thumb up your bum?" asks the magican
"Yes, i can" says little Peter.
The magician waves both hands in front of the boys face and replies...
"Look, that's magic!".