Sniffing Dog

A man boards a plane and is seated next to an Air Marshall and his ‘sniffing dog’.  Soon, the plane takes off and the Marshall says, “Sniffer, search.” The dog walks along the aisle, and stops next to a woman. He then returns to his seat and puts a paw on the Marshall’s arm.
“Good boy,” says the Marshall.
“What happened?” asks the man.
“That woman is in possession of marijuana. We’ll arrest her when we land.”
Once again, Sniffer searches the aisles. He stops beside a man, then returns to his seat, and places two paws on the Marshall’s arm. 
“That man is carrying cocaine,” the Marshall explains.
The dog walks up the aisle again, then races back, jumps into his seat, and poops all over it.
“What’s going on?!” demands the man.
The Marshall nervously replies, “He just found a bomb!”