Hmm in addition to other comments here, one thing that comes to mind is proportions. It's a very large cartoon rounded set of ears when compared to a narrowed, elongated skull. So they don't seem like part of the same piece. Ungulates (eg: goats) have quite long narrow skulls for all those molars.
The thumbnail looked like a mouse and nib to me, but as soon as I saw the whole pice then yeah, could see what you mean. I think if you update the ears to a smaller and more realistic 'rounded wedge' shape, OR round up and 'cute-ify' the skull, they'll match each other tonally.