A suspected World War Two phosphorus bomb dug up by a seven-year-old girl on a Norfolk beach burst into flames when her mother prodded it with a fork.
May Archibald-Green, from Berkshire, was on holiday with her family when she found the device with her metal detector on Holkham beach on Thursday.
She said it "looked like a rock", and began to spark when her mother Judi Green prodded it with a garden fork.
Ms Green said police told her it sounded like a wartime phosphorus bomb.
The area has cordoned off and an Army bomb disposal unit is expected to make sure the device safe later.