After having their 11th child, an Irish couple decided that that was enough, as they couldn't afford a larger bed. So the husband went to his doctor and told him that he and his wife didn't want to have any more children ...

The doctor told him there was a procedure called a vasectomy that would fix the problem but it was expensive. A less costly alternative was to go home, get a large firecracker, light it, put it in a beer can, then hold the can up to his ear and count to 10. 

The husband said to the doctor, "B'Jayzus, I may not be the smartest guy in the world, but I don't see how putting a firework in a beer can next to my ear is going to help me with my problem."

"Trust me, it will do the job", said the doctor.

So the man went home, lit a cracker 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, and placed the beer can between his legs so he could continue counting on his other hand.

This procedure also works in New Zealand and Tasmania.