"Sniffer!!!" joke

A man gets on a plane with his dog.
"You can't bring a dog on this plane", says the stewardess!
"But this dog is special," says the passenger, "he's a sniffer dog."
"Prove it", says the stewardess.
The man clicks his fingers and the dog runs off down the plane. After a minute, the dog reappears, jumps on his lap, and licks his left cheek.
"What's that mean?" says the stewardess.
"It means there's drugs on board." says the man.
"What else can he do?"
The man clicks his fingers & the dog runs off again.
He reappears, & jumps up and licks his right cheek.
"What's that mean?" says the stewardess.
"It means there's a gun aboard," says the man.
"Oh dear!" says the stewardess. That's a bit more serious. "Can he do anything else?"
The man sends the dog off again. This time, he comes racing back, jumps up onto his seat, and craps all over the place "What ever does that mean?" says the stewardess.
The man nervously replies, "Sniffer just found a bomb..."