Here’s a very simple and easy magic trick with very little preparation:
- Fill a bowl with water.
- Cover the top with a thin layer of dust, or something similarly light but visible, like pepper.
- Ask a participant to dip their finger in the centre, which will have no effect.
- Secretly put a drop of washing up liquid or liquid soap to your finger, and dip it in the bowl. The effect is to drive the dust to the edges of the bowl, away from your finger.
It might be obvious to you how this particular trick works. Liquid soap naturally spreads over the surface of the water, so it pushes the light dust away to the edges.
With a bit of showmanship it’s possible to dress this up into quite a nice illusion.