We see that, in John Carpenter's The Thing (and the later prequel movie), that the titular creature is able to assimilate animals such as humans and dogs, and behave exactly like the victim of the assimilation process. But this behaviour-mimicry of human victims is unmistakable from the behaviour of the victims themselves.
The Thing not only looks like people (it is in the foreground of the image above) but is clearly able to pass the turing test - where characters can get into conversations with the creature and be unaware they are not talking to a human.
While the audience is as unaware as the characters about what people have been assimilated until they transform into monstrous entities, a notable exception to this is the "death" of Carter in the 2011 prequel, where we see the creature attempting to allay Kate's suspicions before pleading with her not to destroy it.
This begs the question, are we supposed to interpret all this as the Thing having intelligence and emotions at a human level (perhaps taken directly from its victims)? How does the avaricious entity that is the Thing (which is interested solely in survival and propagation) square with it having... feelings?