Combo-fake Squirt Mustard and Ketchup Bottle Prank Gag Set is easy to use just make sure you stuff the rope into the bottle so its flush to the top, push the bottle hard with two hands, and out will pop the rope to resemble either ketchup for the red bottle or mustard for the yellow. Have fun as they they jump back thinking that its the real stuff. Now just push the string back into the bottle and your ready to try it again. Easy practical joke you can use over and over. By Bwacky