Can you attach a picture? Btw you posted triple. ..
oops trying to attach pic but saying 500 error ill keep trying!!
It looks to me like it's carved out. Depending on how dense and or crumbly your cake is it can be done. Have carved out a shark mouth once quite deep without a problem.
Might also be a layer of RKT in between two cake layers...or a very good edible print...not sure.
If you do if carved out of cake I would do that before you do the fondant, then cover in fondant, cut a hole over the mouth SMALLER than the mouth and tug the yellow fondant inwards. Cover the inside with black fondant and then place in the teeth and tongue.