When Will first wanders upon the alien landing site, he is toting two large carrying bags, both of which are slung over his right shoulder. As the wide shots and close up shots alternate, so does the carrying straps from both on his right shoulder to one on each shoulder back again to both on his right shoulder.
The stricken alien boy is lying in a cave with his arms spread wide from his sides. In a subsequent closer shot, the boy's right hand is now on his chest with his thumb on his medallion.
Will says that taking antibiotics cured his cold. It's a common myth that antibiotics cure viral disease; in fact, they are completely useless, and no antibiotic can cure a cold or the flu.
Smith examines the metallic-looking alien boomerang-ball, saying it obviously doesn't bounce. Will tells him to throw it, and Smith does. It returns, bouncing off of Smith's head before hitting the ground and bouncing away. Obviously it DOES bounce.
John talks about Will contaminating the air when he sneezed, but since John wasn't there to see or hear it, and since WIll never mentioned it, John couldn't have known this.
Since the Taurans were a mute alien race, none of the crew or Dr Smith would have known what the race was called. They communicated to each other via telepathy but Will and the boy never communicated. So there would have been no way that any of the crew would have known what the race was called.
When the alien robot approaches the Jupiter 2, Don states its dematerializing before the crab like device actually does.