^^ WATCH THE VIDEO ABOVE, IT WILL SHOW IT IN ACTION ^^

This trap was made by xXFORBSYXx

How it works
-there is a pressure plate in the corner(on the other side of wall)
-the cacti flows from the farm down to the pressure plate
-the pressure plate activates pistons that connect to the floor
-when the cacti is removed the pistons retract, causing the floor to disappear
-when a player walks past the corner they pick up the cacti that is on the pressure plate so the pistons retract(the cacti glitched through the wall)
-the player killed and their items collect at the bottom of the pit
-then another cacti resets the pressure plate

Pros
-There are no visible pressure plates
-item collection
-self reset

Cons
-you have to fill your inventory to cross (so there is no room for the cacti to go)