Secret Behind Mindreading Crayon
EFFECT: Your friend chooses a crayon from a box, and without even looking at the box or the crayon your friend chose, you can name the selected color. It seems like you're reading your friend's mind!
METHOD: Turn your back and have a friend pick their favorite color from a box of crayons (it helps if the box is brand new). Then have your friend hand you the selected crayon keeping your back turned and not peeking at the crayon! Ask your friend to hide all the other crayons so you can't see them. Turn back around and keep the crayon behind your back so you can't see, but also so your friend can't see.
SECRET: Now we get to the sneaky part. What you are secretly doing behind your back is coloring your thumbnail with the selected crayon. Just a little bit is fine. Make sure nobody sees you doing this. Now bring out your hand (keeping the crayon behind your back) and glance at your colored thumbnail.
THE BIG FINISH: This will tell you what color your friend picked! Now pretend to read your friend's mind by telling him the color he chose! Whatever you do, don't show him your thumbnail and don't tell him the secret =)