Step 1: Step 1
old scissors or diagonal cutter
slip-joint pliers and/or needle nose pliers
bamboo/wood skewers (from the grocer)
Step 2: Step 2
Step 3: Trigger
Note: Don't bend anything outside the yellow ellipse, if you can help it. Otherwise, you'll have to perform some painstaking tweaking of the trigger when you've finished the trap.
...when the trap is set, a length of the skewer will stand straight up in the hole, with a tight fit.
You'll put the skewer piece in later.
Step 4: Step 4
Note: It's also possible to do the following steps before mounting the trap to the can; it's a matter of whatever's most convenient for you.