A trap is an item crafted by means of the tinkering skill with 2 volcanic ash, 1 pack of nails and 1 ignot. When placed down on the ground, after another item, such as, say, a gold piece, it will conduct damage on the being that picks it up, unless they (Rogues) have used the skill "Removing traps" to check its existence and /or de-activate it. The beings can be humans, or monsters.
The amount of damage that a trap can do on a human depends on the tinkering level of the trap placer. The damage is the Tinker level, multiplied by five. So if the player has a tinker level of 6, the damage would be 30hp to a human.
The damage to monsters is less, but can be useful. The damage to creatures appears to be calculated with the formula (Tinkering x 5)/4.
Creatures that will not pick up traps include: Bears, Dragons, Gooeys, Rats, Sheep, Trolls, Bracken (incomplete). All other creatures will pick up traps.
NPCs (such as guards and shopkeepers) and beasts have a Tinker level of 3. Thus, if passed a Trap created above level 3, they will "metabolize" the Trap, down to level 3.
PS: Traps can be made at level 5 tinkering, but if you buy/trade from another character when you put down, the trap will recognize The Tinker level of the Character than dropped.