A good many dogs think a cat's butt is a Pez dispenser. It's a mystery to me.

yeah typical cat parking its butt right in the face of a, well, dog in this case

Yeah, I had a roomate whose dog would clear out the litter box and th ed n follow the cat around waiting for more.

What colour is the other one? Maybe its darker and therefore the brighter one will radiate more heat energy. You'll notice the cat is very dark making it a good absorber of infrared.

Nope, he's gray. It could be that the cat prefers the lower end of the spectrum, and doesn't want to deal with higher frequencies -- I could be wrong but doesn't radiative transfer become less efficient as frequency goes up?

Cat heat goes down, dog heat goes up. This is pretty basic.