I loved that one! He can take the form of other people but is hive-like or something so if you heat his blood the host goes nuts? Something like that anyway. Kurt Russel. The claymation was excellent: cult classic.
That's mostly from John Carpenter's The Thing, the blood reacted to heat as our protagonist's test for detecting infected hosts, not causing the host that was tied up to react, that was just the thing transmogrifying. There's also a Pournelle novel where a research team lands on a green, human inhabitable planet and a native species looks something like a monitor lizard but can engage a hyper mode that speeds up it's metabolism so it generates a lot of heat, this is to enable it to run like a cheetah with the strength of a gorilla or something like that IIRC.
