I believe it was detonated by a teleporting Chihuahua. It is well known that this breed of dog has those abilities and me being the owner of one have in fact witnessed it teleport on many occasions. Many times I get up to let the dog out when it is barking at the door only to find there is no dog there and to see the dog laying down on the sofa as if it had been there all along. It also has appeared right in front of my fox terrier as soon as he was about to chew on a rawhide to have it quickly snatched away before he even gets a single chew.
This documentary on youtube will prove that Hitler did in fact use Chihuahuas in combat.