"Laughing Horse ...." joke

A dude walks into a pub with a horse and challenges anyone to
make his horse laugh for $50. Everyone at the pub has a go at
trying to make the horse laugh without any luck.
Then the dude claims to be able to make his horse laugh for
$100. Having got the go from the pub dwellers, he whispers
something into the horse's ear and the horse starts laughing,
much to the amazement of the people in the pub. The guy walks
away with his $100.
A week later the guys arrives at the same pub and claims to be
able to make the horse cry for $100. He then walks his horse to
the mens room and comes out in half a minute with the horse
crying. He then collects his $100 and walks out
On they way out the bartender approaches him
Bar Tender: How on earth did you manage to make that horse
laugh? ?
Guy: I told him my dick was bigger than his
Bar Tender: Okay then how did you make him cry? ?
Guy: Easy, I showed him my dick