When Samantha asks Andrew about his son he states that he will be 6 yrs old tomorrow when his birthday is actually that very day because the night before he called his son to wish him a happy birthday and he said he was calling then because he wouldn't be able to call tomorrow.
The Pre-Columbian pyramid the two protagonists climb is located in a jungle setting. From the top of this pyramid they are able to view the border between Texas and Mexico, which is nowhere near any jungle.
At the start of the film, in "San Jose, Central America" we see a sign showing "US Border 200km". The shortest distance between the Central American border (Mexico/Guatemala) and the US Border is approximately 1,700km.
The scene where Samantha is about to board the ferry is located in Cancun on the southern part of Mexico but the map showing the infected zone is close to the border with the United States on the north.
Before Andrew buys train tickets, he looks at the giant wall map of the Infected Zone. All the train line stops have British names like Southhampton Central, Salisbury and Portsmouth all in their respective UK locations.
A cephalopod mollusk (or even a vertebrate animal) of that giant size would have no ability to walk or move on land. It would be crushed by it's own massive weight.
Since the creature is of extraterrestrial origin, however, its alien anatomy might have certain adaptations that allow it to walk on land without being crushed by its own weight.
As the couple arrives at the town and the camera travels across the town and over the evacuation sign, right after the goof with the pickup-truck seen at the distance, they look at the town and a person can be seen walking away from the white car in the distance. Another result of shooting in open locations.
When the two characters arrive at the deserted town on the US side of the border, and the camera pans the town and focuses on the evacuation side, you can see a pickup truck driving down the road. (This is likely the result of using open sets for filming, which allowed for the shooting areas local population to be accidentally captured in a shot.)
Toward the beginning of the film when Sam and Andrew are first attempting to purchase ferry ride tickets to the U.S., the worker informs them that tickets currently cost 4,000 Colones due to high demand. A Colón is the currency found in Costa Rica and 4,000 colones is equivalent to about 8 U.S. Dollars.