Spitballers have weakpoints in their mouths?

Did they always have this? Is this a bug?

[@PikeRondel]

It kind of makes sense, I would imagine that the inside of its mouth is weaker than the outside of it's body, excluding the weakpoint, and it seems too far away from the normal weakpoint to somehow be overlapping so I would assume it's intentional?

[@BCKes]

Can you give the name of the mod that changes sound of the m1k?