Fun.
Learned in fifth grade although we usually did it with chalk:
(1) Make a fist with your right hand
(2) Press the outside edge of your fisted hand onto a stamp pad and then onto a wall (or whatever.) This leaves a very realistic impression of a small foot.
(3) Press the tips of your middle three (or four) fingers into the stamp pad and deposit that image just above the previous hand print. This completes an amazingly convincing image of a small three (or four) toed foot.
(4) Repeat, using your left hand and fingers, and make several images going straight up the wall.
The final impression is that of a small three (or four) toed humanoid critter walking barefoot up the wall.
The same may be done on horizontal surfaces, and, if soft enough, in dirt, without using any coloring matter.. Other coloring systems besides an ink pad may be used (like finger paint, or dirty hands from fixing the car.)
(5) Secretly remove yourself from the area, lest someone think you were the childish one.
(6) Wash your hands as soon as possible, lest someone think you were the childish one.
(7) Don't deface public property with this --they will have your fingerprints, you know.
Terry, ("Moving into my [giggle-giggle] fourth childhood"), 230RN
ETA: Make that "fifth" childhood.)
ETA (2) Hey, I'm 71, I got an excuse.