One of my favorite illusions, eating a balloon takes some practice and an attention to preparation. This trick is best done when your audience is at least three to ten feet away, as the escaping air of the balloon can ruin the trick. to combat this you may choose to play music over the illusion.
Before the illusion pierce a small hole at the opening of the balloon with a safety pin, thin nail or needle. Be sure to make the hole closer to the body of the balloon than the opening to make tying easier without blockage. It is advised to have two or three balloons ready in case the first one malfunctions.
During the show inflate the balloon fully. Cover the hole that was made earlier either with a finger or, depending on the location of the hole, your mouth. Tie off the balloon, making sure you do not block the hole as you do so. Take the end of the balloon without the knot and put it in your mouth. Poke your tongue into the balloon. Slowly and carefully push the balloon down, onto your tongue.
Once the balloon has been completely deflated a small ring of rubber will be left. Hide this in your cheek until you can remove it without the audience seeing. If you push the balloon too fast or hard it will start to bubble at the top. This can not only cause the end of the trick to go wrong but it could give the whole thing away. If this happens stop, let the air escape the balloon, then continue.
Be careful not to swallow the deflated rubber once your illusion is complete.