A doctor went to a store during his lunch hour to buy cigarettes at a local store. When he comes out, he is surprised to see a man sitting on a bench eating dog food. Approaching the man, the doctor says:
"Excuse me, sir, but I could not help noticing you eating dog food. As a doctor, I feel it is my duty to warn you of the potential health hazard of such a diet."
To this, the man answers simply:
"Look Doc, I've been eating dog food for a year now, and I've never been healthier."

Now curious, the doctor decides to check upon the man everyday during his lunch hour. Surely enough, everyday, he can be seen on the same bench eating the same brand of dog food. Then, one day, the man is gone. Curious, the doctor asks a man whom he had seen from time to time in the park what had happened to the man who ate dog food. The man informed the doctor that he was dead. Upon hearing this, the doctor proclaimed:
"I knew it! I knew that eating dog food would finally kill him!"
"No Doc, that's not it at all. He was sitting on the curb licking his balls when a garbage truck backed onto him."