In article , David in Normandy
wrote:

how do you know where to put them?

Look for the tunnels leading to a molehill - they may be obvious as the
turf will have lifted slightly above them; if not, poke around
carefully with a sharp stick or cane to find cavities an inch or two
below the turf, being careful not to leave the surface broken since Mr
Mole doesn't like sunlight. Make a small indentation in the roof of the
tunnel and position the trap on top of it, straddling the cavity. Mr
Mole will scurry past the trap's fixing spikes and will be forced by
the indentation to push upwards at that point to trigger the
portcullis.