What you need:

1 x hard boiled egg

1 x glass bottle with a wide neck (just wide enough to sit the egg in)

Boiled water from the kettle

Steps:

Pour boiling water into the bottle to about a third of the way up.

Place the hard boiled egg so that it sits in the neck of the bottle.

Watch and wait. You will notice the egg gets shifted by the hot air in the bottle, this is when the hot air expands and escapes a bit.

The egg will eventually get sucked into the bottle.