A candle is placed in a shallow dish with water and is lit. A glass is put over the candle.
After the candle extinguishes the glass fills with water.
Why does this happen?
Whilst the candle is burning, the air inside the glass heats up. After the candle extinguishes, the heat is taken away and the air cools quickly. This results in a vacuum/negative pressure which balances out as the water enters the glass.