It's possible to glitch through walls using the feather item If you enter the Cat pipe at the end of the room with the feather on full speed (by that I mean: Activate the feather while on the ground, and then double jump while the feather is activated. Using the feather while on the ground gives you extra speed and while using it after a double jump mid air it gives you longer in-air time, but at a reduced max speed) and hold left during the loading screen you will be displaced a bit in front of the room entrance, and thus it's possible to get inside the walls. This is completely useless on the Cave level since you can't enter the cat pipe to the next room, but could be used for something eventualy (Since for example the 3rd room secret Catpipe is just off-screen and moves to a random location on the map when the room is cleared; a room could be skipped and thus some time saved)