One of my favourite 'makes' ever was a gag. I made it with one of those flightless golf balls. Through the middle I passed some static cord and did a little creative knotwork to both hold the ball in place and create a thicker section of rope so it didn't cut into the side of my playmates mouth too much. It was simply to put on just pop it in the mouth and tie behind the neck. With all the holes in the ball my partner could breath but it also induced loads of saliva which would have anyone dribbling uncontrollably.