Only One Arm

A Kerryman was boasting about his brother's exploits in the Army.
'He was the finest soldier of the day', he claimed. 'Although he had only one arm, he used to rush into battle without a single weapon. His favourite method of disposing of the enemy was by banging their heads together'.
'How could he bang their heads together if he had only one arm?' asked a listener.
'In the heat of the battle', replied the Kerryman, 'my brother forgot all about that'.