I don't see this line number? Nor do I see any code that relates to this behaviour.I write programs for a living.
I don't think it's a case of this functionality being implemented by TWI, I think it's just a case of it being possible to headshot all specimens unless specified otherwise, and with the Flesh Pound it simply isn't specified otherwise. Why it can only be done when he bows his head, I'm not sure.
And try not to triple post please, there is an edit button.