Also how big is said goddess? Maybe the imagery was supposed to be similar to Maui being like water. The path isn't direct from mouth to eurethera, but maybe he can be absorbed through barriers as well.

Also... Why did we skip over how that would make humans immortal?

Well this cooter has teeth (and is a grinder we have learned) so one imagines it has a connection into the digestive system, but then if he knew that, he'd probably have known to avoid the teeth.