If you're plagued by gophers in the yard, then you will love this trick. Dry ice is available at grocery stores and specialty food suppliers. Some industries also require the use of dry ice. It doesn't melt, it sublimates, turning into carbon dioxide instead of water. Gophers hate carbon dioxide.
Use landscaping flags to mark the location of every gopher hole in your yard. If your yard is very close to your neighbor's you may need to coordinate efforts with them, so that the gophers don't run for cover temporarily in the neighbor's yard.
Put on a heavy insulated glove before you touch the dry ice. It's very dangerous to touch it with your bare skin, you can become injured. Also wear protective eye goggles whenever you have to break dry ice.
Use a chisel and a hammer to break the dry ice into 1-2 inch chunks. If you're lucky, your brick or cube will come pre-scored, but this isn't often the case. They don't need to be exact, but 1-2 inches is a guide.
Place a chunk of dry ice into each gopher hole as deeply as you can reach with your arm. Immediately cover the hole with dirt.
Repeat with the rest of the holes as quickly as you can. The dry ice will sublimate (not melt) and carbon dioxide will sink down into the holes, cutting off the oxygen supply for the gophers and gently sending them to sleep. Forever. Mwahahahahaha.