First the possum is lured by the smell of some sweet bait mixture.
There it is, inside that thing attached to the trunk of this tree! Gripping the tree trunk, the possum pokes his pointy head up into cone-shaped plastic portal with the lure at the top. He gets the barest taste of the lure before he triggers a punch, powered by a CO2 canister, which gets him in the back of the skull. He never knows what hit him and falls out of the tree - dead before he hits the forest floor.
Then the trap automatically resets. It's not uncommon for one trap to account for five possums in a single night and the CO2 canister is good for 20 kills. Because possums are only a pest in New Zealand, Goodnature have made a version that nails rats and stoats as well.
In a trial of two rat traps in Indonesia each trap killed seven rats in one night.