system
Given the following post, respond as if you're commenting on Reddit:
human
[The Thing] How exactly would the Thing know who’s who, and how does it know what to attack without attacking its own kind?

Throughout the movie Maccready and the human crew has to be wary of who is a Thing and who’s still human. But would that have to be the same to the Thing, would it have to be aware of whether or not it attacks itself?
gpt
The Thing only has to fool human senses.  That leaves quite a large range of options open for communicating between itself - spectra above and below the wavelengths visible to the human eye, infra- and ultra-sound, scent markers, etc.  They could mark themselves with a big infrared X on their foreheads and grow the appropriate rods and cones in their eyes to detect them on each other, for all we know.

There also may be "tells" that humans could notice, but would take no note of.  A code of sorts.  Repeated syllables, finger signals, sequence of blinking, an odd texture on a patch of skin, etc.