After having their 11th child, a Tasmanian couple decided that was enough, as they could not afford a larger bed. So the husband went to his doctor/veterinarian and told him that he and his wife/cousin didn't want to have any more children.
The doctor told him that there was a procedure called a vasectomy that could fix the problem but that it was expensive. A less costly alternative, said the doctor, was to go home, get a firecracker, light it, put it in a beer can, then hold the can up to his ear and count to 10.
The Tasmanian said to the doctor, "I may not be the smartest man in the world, but I don't see how putting a firecracker in a beer can next to my ear is going to help me."
"Trust me," said the doctor.
So the man went home, lit a firecracker and put it in a beer can. He held the can up to his ear and began to count: "1, 2, 3, 4, 5" at which point he paused, placed the beer can between his legs, and resumed counting on his other hand.
This procedure also works in New Zealand.