It wouldn't be Halloween without some exploding pumpkins. In the top jack-o'-lantern, iron oxide and aluminium powder react to spectacular effect. Once set off by a strip of magnesium, which provides enough heat to get the reaction started, the temperature inside the top pumpkin rises to around 2000 degrees Celsius. At this temperature, the iron melts and is spewed out in a rain of fire, and flows out as a river of molten metal into the poor head below. This is more than enough to set off the gun cotton in the second pumpkin, which bursts into a healthy fireball.