Hand Trick

A fellow played the following trick on a Kerryman.
'Listen', he said, 'punch me on the hand as hard as you like', placing his hand up against a brick wall.
The Kerryman swung his fist but at the last moment the fellow pulled away his hand, and the Kerryman's fist went crashing into the brick wall. After a good laugh, the Kerryman decided to try out the trick on his friend.
'Listen', he said, 'punch me on the hand as hard as you like'. He looked around for a wall but he couldn't find one.
'We would really need a brick wall to do this trick properly, but never mind, I'll hold my hand in front of my face'.