That'll work too, but propane cost too much $$$ nowadays, much cheaper to use car exhaust. My Dad, told a story, when America was a different country, he and a group of his friends, at the age of 12, would take their .22 rifles, and a can of gas down to the local dump. They would pour about a cup of gas into one of the holes in the trash heap, wait a minute or so, to let the vapors seep into the heap. Then, toss a match in the hole. He said the whole heap would jump, then the rats would POUR out of it. He and his friends would blast away with their .22s and have a ball. Dad said his dog, who usually came along with them, didn't know which rat to grab first. Can you imagine today, a group of kids carrying rifles down through the middle of town? They would probably have the SWAT team come down on them.