Gobstoppers, (aka Jawbreakers in Canada and the US), are a type of hard candy made up of a number of layers, each layer dissolving to reveal a different colour and/or flavour.
In 2003, nine-year-old Taquandra Diggs from Starke, Florida, suffered severe burns, allegedly from biting down on a Wonka Everlasting Gobstopper that had been left out in the sun. Diggs and several other victims’ families filed lawsuits against Nestlé for medical bills resulting from plastic surgery as well as pain and suffering; the matters were later settled outside of court for an undisclosed amount.
In 2004, Discovery Channel’s MythBusters, tested the allegation in a microwave and indeed found that the candy would explode with heating. The reason? Gobstoppers are formed from multiple layers of sugary syrup surrounding a solid candy core encased in a hard outer shell. That jawbreaker architecture can cause a temperature differential, meaning that the internal layers can heat up faster than the outer ones. MythBusters crew members Adam Savage and Christine Chamberlain received light burns after a gobstopper exploded. The explosion effect however, was not replicated without the use of a microwave. (Discovery.com, Wiki)