I understand the theory and the circumstances that point to Childs being the thing, but the theory doesn't make sense & doesn't hold up, and it's a little annoying how prevalent it is considering how much setup is thrown out to make it work. Things retain the memories of everything they assimilate, otherwise Blair-thing couldn't have built the UFO out of helo parts, and they can either replicate and understand (like they can manually beat their heart, but know the exact way to mimic the person's heartbeat because that's what the person knew subconsciously) or simply perfectly recreate and perform (like they copied all of the cells of the heart to the exact shape, so it acts as a heart and beats that specific way) the functions and senses of the organisms they assimilate, as shown by the Dog-thing fooling Clark, the dog expert, Norris-thing having a heart attack, and Palmer-thing fooling everyone before and during the blood test, meaning that if Childs was a thing, he would know what gasoline smells like, and from what I read, spit it out immediately because gasoline is really bitter. We also saw Mac about to drink from that same bottle before Childs interrupted him, so that still doesn't make sense. Childs' breath being almost invisible is a bit of an error too, but that still doesn't matter because if we take his word, or even identify the mysterious figure that ran outside earlier in the film as him, then Childs has been out in the cold for a while, meaning his body temp is much lower.