I've been thinking about this a little. I have heard of two types so far but not very sure. One that have died then reanimate, and ones that turn. Is there a possibility the smart ones are those that just turn. Being that there higher brain functions are still working at the time of infection, but the ones that are just "regulars" are those that have died and come back because the basic animal instincts are the only that were reanimated within the brain. We already know they don't feel pain so that tells you right there some of their bodily functions don't work. Sound to me it's a mutated form of the "old school" zombie virus we are all use to in the past. Makes me think of Walking Dead meets Resident Evil meets I Am Legend the movie. Its a new type of Zombie.

As for the heat signature I think there is a big difference between them. The "turned" ones may have a higher temp than "regulars" due to energy expenditure, and the "reanimated" one may have a very low temps due to energy expenditure but loss of more bodily functions or abilities. But either way I think they have a lower body temp than a regular human. Either that or the body temps are much higher than humans and they are trying to keep themselves cooler which is the reason they started colonizing the ice arena, but when the refrigeration equipment failed it all thawed out. Don't know there are to many factors.