A bulldog in the greyhound race

Heard this one from a friend:

So, a man has a bulldog and goes for a walk in a park with it. There is a greyhound race competition. The bulldog says:
"Come on, man, sign me up!", to which the owner reluctantly says
"What the hell bulldog, you won't make it."
"I'm sure I will, sign me up!"

Thr owner signs the bulldog for a race. All the dogs are at a start line, along with the bulldog. The first lap starts, all the dogs run as fas as they can, then the first lap finishes and bulldog is last. The owner shouts from the audience:
"Told you, you're last!", to which the bulldog just nods and says
"Easy man, easy."

Second lap isn't much different from the first. Bulldog just runs at the end like he doesn't care. The owner gets annoyed and shouts from the audience:
"What the hell, bulldog!?", bulldog just nods and says:
"Easy man, easy..."

Third (and also second to last) lap, nothing changes and bulldog is still last. Now the owner is angry he wasted his time, and shouts from the audience:
"What are you doing, bulldog!? You told me you would make it!", to which bulldog just nods and says:
"I will. Easy, easy..."

Right at the beginning of the last lap the bulldog starts running with a godlike speed, at half of the lap he is aldready seond, 3/4th into the lap he is first and no one is close to him. He runs gloriously and the owner is amazed. Then suddenly the dog just falls on the ground right next to the finish line. He is disqualified and receives no points.

After the race, the owner approaches the bulldog, he's surprised, amazed and angry at the same time and asks:
"What the hell happened, bulldog!?" - bulldog just looks at him and says:
"Shit, I don't know."