Prot removes his glasses and lays them down so that the top of the glasses are laying on the table. Later, when Mark Powell rushes in, the glasses are lying right-side-up and facing the opposite direction.
When Mark Powell's daughter is first seen, she says that she lost her front tooth. The next time she is seen, she smiles and still has her baby front teeth.
When Prot arrives at David's house for the barbecue, he meets Rachel and shakes her hand. The only people in front of him are Rachel and the two children, but the reflection in his sunglasses shows everyone even though most of the people in the scene are behind him.
When Prot is speaking to the dog at the barbecue, he asks the kids to come closer, which two of them do - the older girl with pigtails on the left and the boy on the right. Rachel holds her young daughter back initially. In the next shot, the younger girl has now moved over next to the boy, and in the following shot after that (where the girl says "no way"), the older kids have switched places and the young girl is now between them.
When Prot visits the doctor's home his sunglasses alternate between plain and silvered between shots.
Dr. Powell makes an important discovery based on a closer examination of Prot's pencil stub. He gets an area code and the start of a name which leads his investigation in a new direction. However, the printing on the pencil would typically never be oriented to begin at the eraser end. If the text had instead ended at the eraser end as expected (and he got the last part of a phone number instead of the area code), Dr. Powell would not have been able to narrow down his search.
When the doctors are meeting, the film crew is reflected in the shiny silver coffee pot as one of the doctors pours coffee.
The story takes place in New York, but in one scene the Westin Bonaventure Hotel in downtown Los Angeles is visible through the office window.
At 1:29 in the movie, when Dr. Powell drives from the airport to Guelph, which is supposed to be in New Mexico, it shows him viewing the Park City arches at Arches National Park in Moab, Utah.
When Dr. Chakraborty is talking about Prot's vision, he describes him being able to see ultraviolet at 300-400 ångström. Generally in the context of vision, ultraviolet wavelength is ~280-400 nanometers or only 2800-4000 ångström.
After Dr. Powell discovers the pencil and sees the area code on it, he makes a call (presumably to Information or the like) and asks "Is this area code 505?" Since he would have had to dial "505" to reach the party he talks to, this is a silly question.