The sort like two blunt secatuers held three to four inches apart by a horizontal bar linking each (same side) pair of blades, springs push the handles apart, closing the blades. Trap is set by closing the handles and putting a metal O with "shoulders" between the horizontal bars using the shoulders.
As mole pases through the blades from either direction he dislodges the O the springs shut the blades an break his spine.
You can tell if it has sprung without re-opening the tunnel, cos the handles have moved.
NB the word blades is used as description of shape as the part concerned is 3mm galvanised steel bar.
