This Halloween, try the classic science experiment with the candle under a glass with a vampire twist! This simple spooky science experiment is perfect for the holiday season! If you little scientist asks why the vampire sucked all the blood (coloured water), here is a simple explanation: the candle is heating the air inside the glass; it expands and gets out (you can see air bubbles when you place the glass in water). When the candle goes out, the air inside starts cooling down and shrink back to its original volume. Water blocks the way for air to come in, so air pressure outside pushes on it, causing it to go into the glass.