Director of photography Dean Cundey and effects artist Rob Bottin apparently were at constant odds with each other when it came to how to film the effects for 1982's The Thing.
Bottin just finished The Howling and thought his work would be better showcased in shadow and backlight. Cundey preferred that all the alien shots be shown in stark spotlight. Bottin finaly won, and I think we all benefited from the result.
Maybe that's why the "dog transformation" scene work so well and can be viewed so many times. Each viewing gives you a little bit more of the creature.
Was that an eyeball???