Presumably causes an explosion
Elephant and Castle
The Office for the Detection and Confiscation of Counterfeit Defensive Spells and Protective Objects got wind of one of these in Elephant and Castle in July of 1996, but it was sorted out by the Magical Law Enforcement Patrol before they arrived on the scene.
Tragedy in the Dumbledore family
While Percival Dumbledore was imprisoned and his sons Albus and Aberforth attended Hogwarts School of Witchcraft and Wizardry, his wife Kendra took care of Ariana. Rumours spread by people such as Muriel and her cousin Lancelot suggested that Kendra was keeping her "Squib" daughter locked up in a cellar. When Ariana was fourteen years old, she lost control of her magic, and the explosion caused by a Backfiring Jinx killed Kendra.
- Harry Potter and the Half-Blood Prince (Mentioned only)
- Harry Potter and the Deathly Hallows: Part 1 (Mentioned only)