Jack Knife
A jack knife is a basic knife used by hunters and fishermen with two blades that flip open from the handle, which is usually made of wood. This isn't your traditional can opener, because it consists of just a basic blade. These blades are used to open cans by wedging the tip under the edge of the can and gently prying up the top of the can. A pen knife has a similar type of can opener.
Multi-Purpose Knives
Multipurpose knives, such as a Swiss Army Knife, are much more common and popular. These knives feature several different blades designed to help in a variety of situations. A few common features include scissors, tweezers and a screwdriver as well as a can opener. This type of can opener is fairly basic and consists of a curved piece with a sharp, pointed edge. The pointed side sits on the side of the can and when you exert pressure, it punctures the can. You slowly work your way around the edge of the can until the lid comes up.
Folding Can Openers
Some pocket knives contain a feature known as a folding can opener, which is similar to the ones the U.S. Army issued during World War II to soldiers working in the field. The blade of the can opener folds flat and sits inside a metal piece, which slides into the knife. When you need the can opener, you slide out the piece and unfold the can opener. It too is basic and involves slowly puncturing the lid of the can until you can pull it off completely.
