Where's the Critical Hit spot on Abaddons? Found in Bounty of Blood?

Where's the Critical Hit spot on Abaddons?

Is it their mouth? Doesn't seem like it... Or is it just really tiny?

Or do the Mounts have different one from the regular ones? Not like I've found the point on those either.

Or are the one of the rare enemies without one?

Or is it on their tail??