The Old Norse, hereinafter referred to by the more common appellation of "Vikings," held to many customs that, to us, would seem strange. Some of these customs, indeed, remind us more of a modern biker- gang than peoples we would consider "civilized."
Perhaps the prime, and most well-known, example of such a thing was the "blood-eagle," that struck such terror in the British Isles.
Not as well known, however, was the practice of "brammage," or, in Old Norse, "brammagr."
It was originally done by the berserks of both the Norse and the Danes, and excited both awe and disgust in the ranks of the enemy.
As the armies formed up, the berserks would push thru their lines, and stand between the armies, not unlike skirmishers, and proceed to beat upon their own helms with the flats of the swords. If the berserks wore no helmets, they would beat upon their unprotected heads. This was the prelude to the usual shield-biting, jumping up and down, foaming at the mouth, and screaming insults about the ancestry of the opposition.
One can only imagine the sight, and easily see that such behaviour would strike terror into the minds of the opposing forces.
However, the striking of the head, whether protected or unprotected, would tend to damage and/or slow down the thought processes eventually, and so it did. The survivors tended to be "a bit slow."
The only remaining evidence of this practice is commemmorated in a fragmentary saga, scribed in runes on the carcass of a moose currently in the National RjiksMuseum.
We find that the Brammagr-rite entered the English language, due
to the Danish occupation of Britain, and thus, we see the expression
used, while pointing or striking the head with the hand, "Dane Brammage!"
to express stupidity.