The legal trap is a chess trap in the Italian opening. Traps are fun to look at because they lead to a checkmate in a way you may not have expected. You can see the moves in the picture that lead up to this check mate and there’s a great video on this from the chess website.
If you want to see the moves played I’ve also included a gif file below which animates the moves.
Essentially white opens with the Italian and if black plays the Philidor defence and then moves the black bishop to g4 pinning the knight then the trap is unleased.