Because every time they go to the starting gate they're reminded "They're Off!".
Cleaver! EDIT: Also Sharp, knew about this one but I like Cleaver better.
Bob.
A neighbour!
None. Horses are not known to use operating systems nor computers for that matter.
A Cheetah.
Because the horse hugs the rails the jockey puts his arms around the horse and you can kiss your money goodbye!
You remind me of someone
Because it reminded him that time was moving forward.