Spoilers for the ending of The Thing from 2011.
When Kate and Carter emerge from the spaceship, Carter is still wearing his flamethrower, like he was when he entered the ship.
However, he ditches the flamethrower and gets into the snowcat first. Of course, Kate then realizes he is a Thing who plans to drive the snowcat to the nearest base to get more biomass; she picks up the flamethrower and torches it.
Why did the Carther-Thing put itself in that position? It was alone with Kate, which was its modus operandi when infecting people before it was found out (like when the Juliette-Thing was alone with Kate earlier) and it had the flamethrower.
Why not infect or kill Kate at that point, instead of getting rid of its human weapon and getting into a vehicle with her? Even if it did manage to infect her en route without being found out first, assimiliation is a messy procedure, and it already crashed one helicopter while trying to overtake its passengers.