Brittney seems to have a brunette scalp under her blonde hair, and when your doing her doggystyle, it produces some unfortunate visuals.
I only bring such a minor issue up because I suspect it would be really easy to correct. 5 minutes of the devs' time in photoshop to change Brittney's scalp bitmap from brunette to blonde. Even if the results are a little messy, I'm sure they'll be much less jarring than they are now.
You get an idea of what I'm talking about from this still, but IMHO, the actual animation is much more jarring. As she tilts her head, you can see a strange gap appearing between her head and neck, and for a moment it looks like her head's about to fall off. Totally kills the immersion.