The bow trap is an effective trap for larger prey. But it's important to note that the trap won't differentiate between animals and humans. So always approach the bow trap from behind and never set it in an area where other people may stumble across it.
Something to keep in mind when building a bow trap -- or any trap that requires some construction -- is that animals notice changes in their environment. You may prevent them from noticing your trap if you build it away from the area where you plan to set it. After you've handled the materials, they'll have your scent on them. To mask the scent, try coating the materials in mud.
The first step of building the bow trap is to construct the bow. Use a sapling and twine for this. Then, anchor the bow to the ground from the back, using short but sturdy sticks. Use a stick with a sharpened end as your arrow. Place this stick in your bow and then drive two sticks in the ground, one on either side of the arrow stick, to help it fly straight. Connect a trip wire to the back of the bow, pulling the bow back. Drive another stick into the ground to run the trip wire around, passing it in front of the bow. When your prey trips the wire, the arrow will release.