Fable the lost chapters - Killing the balverine that bit the trader

This trick is on the Trader escort quest.

When you start the mission walk up to the rails on the side opposite to where you find the trader, and walk around until you can see a balverine standing there

Then pull back your bow and try to shoot it in the head, with enough accuracy ( or if you hold the string back long enough) you can take its head off.