Perhaps it is because many people have a deep fear of serpents and snakes. Or maybe it was a backup weapon.

Actually to my knowledge the reason men charged into battle naked was because of the drugs, to instill fear in the enemy, and I believe the main reason is because they did not need armor or shields because the power of their faith protected them.

I remember reading about how some vikings or nords or people of the sort charged into battle shieldless for this exact reason: their faith was the shield that protected them.