Forest booby trap

How devastating a trap do you need this to be? Are you killing off characters, scaring them or entrapping them for further plot developments? All three can be done.

A body works great as a counterweight to hold down a lever, depress a pin or have something tied to it. It also makes people want to get in close to see if the person is "okay" so you can reliably bet on people getting into close proximity of the body.

In this case, go watch some movies and you'll see loads of inventive traps that can be made using human bodies.

Dig a pit trap and set the body on the other side - a person walks up and falls into the pit. Put a tripwire on the body so when it gets moved it triggers some other trap. Have the body weight holding down a grenade arming lever or the pin to a landmine.

If one were trying to snare a fox, then there would be a loop of rope (tied to a springy tree) with the body holding it and set so that when the body was moved the rope would be pulled by the springy tree. That might even work for a fox or a bear, but I think that the best idea for bandits trying to slow pursuers would be to have a hidden pit and the body behind it, so that pursuers would fall into the pit on the way to inspect the body. That probably wouldn't catch all of the pursuers, but it might put some out of action for a while. Or maybe moving the body would trigger explosives; they used that in Iraq.

All sorts of nasty things can be done with whippy branches, sharpened stakes and a bit of rope. When it comes to this, movies can actually be quite accurate.

Trip wires (or cords) can set off other things besides explosives. In a medieval society, a cord could set off a crossbow.

Another possibility would be a deadfall - that same cord causing a heavy branch or small boulder to fall from the tree above the body.