"Moose Love Call" joke

Two hunters went moose hunting every winter without success.
Finally they came up with a foolproof plan. They got a very
authentic cow moose costume and learned the mating call of a cow
moose.
The plan was to hide in the costume, lure the bull, then come out
of the costume and shoot the bull. They set themselves up on the
edge of a clearing, donned their costume and began to give the
moose love call.
Before long their call was answered as a bull came crashing out
of the forest and into the clearing. When the bull was close
enough, the guy in front said, "OK, lets get out and get him."
After a moment that seemed like an eternity, the guy in the back
shouted, "The zipper is stuck! What are we going to do!?"
The guy in the front says, "Well, I'm going to start nibbling
grass, but you'd better brace yourself!"