The Dutch public have been warned it is "strictly ill-advised to lie down on a bomb", after a man did just that for about three hours.
The man came across an unexploded World War Two device while gardening in the town of Venlo on Wednesday.
When it started whistling he covered it with his body, apparently trying to limit the damage.
Nearby residents were evacuated and the device proved harmless. The man was treated for symptoms of hypothermia.
The device was variously described as a grenade or a shell.
Security services spokeswoman Veronique Klaassen told AFP news agency the man had covered the device with sand but when it started whistling he put his body over it.
She said he dared not move and rang emergency services on his mobile phone.
Ms Klaassen told AFP it appeared the defence ministry bomb disposal team must have come from some distance away as it did not arrive until about 01:00 on Thursday (midnight GMT) to free the man from his "delicate position".
Surrounding areas were evacuated, affecting more than 100 people, but it transpired that the device no longer had any explosive material and they were allowed to return to their homes. What caused the whistling remains a mystery.
The man was taken to hospital suffering from the extreme winter cold.
Ms Klaassen said: "It is strictly ill-advised to lie down on a bomb. The best thing to do if you come across an explosive device is keep your distance and call the police."