He noticed Na had a crisps bag, so approached her to see if she might be persuaded to share the snack. The bag had no crisps...it was full of jungle fruits Na and Aay had picked up on the hill behind the temple. Na showed the bag to Bill, so he could work out the situation for himself, and was even prepared to share the fruits. Bill put his snout in the bag, and checked it out. He then withdrew his nose from the bag, took a step back, then leaped forward and whacked Na hard on the kneecap with his battering ram forehead.
The message was clear..."Next time, bring crisps!'.
Na has a large, purple bruise on her knee as a memento.