im afraid it is incorrect, a laughing skull would look like the same thing as a talking skull on its highest opening. maybe you shouldnt make the teeth rows curves like that, but mix the skull with cartoon ( where they have cheeks ).
currently it looks like the lower jaw had a rotation of 45degrees seeing how the teeths are placed. you will probably not change it, but im trying to help.
nice contrast with the 2 colors too, but it might be hard to see when the camera doesnt have an upclose of the flag