For the deadfall trap, you'll need three small sticks and a flattish rock. Lift one side of the rock and prop it up with the sticks. But the sticks are joined together in an odd way -- in the shape of a number four. One stick is staked in the ground and the others are tied to it to form a sideways 'V.' If you don't have string, you can cut notches in the sticks with a knife to hold them together.
When an animal runs into the sticks, it brings the rock down. Test the deadfall several times before you set it up to catch prey. It shouldn't take much pressure to release the rock. You don't want a stiff breeze to knock the sticks down, but you also can't expect a tiny rabbit to shove the sticks.
A deadfall trap is easy enough to build. The trick is convincing the animal to go under the rock. Baiting is an effective way to draw in prey, but it requires some consideration. You don't want to bait your trap with berries or nuts that are widely available in the area. On the other hand, using corn or other domestic food sources may make your prey uneasy. There's one bait that's effective, draws all sorts of animals in and is readily available -- salt. Sprinkle some around and under your deadfall, and your prey will come to lick the salt from the ground.
A deadfall is an effective trap for smaller animals, but what if you want to catch something big?