Goof (errors made by characters, possibly deliberate errors by the filmmakers): Tom Mason refers to "the Scots against the British at Stirling Bridge" as an example of a weaker force defeating a stronger one. He should have said the Scots against the English as British refers collectively to the Scots, English, and Welsh (and for some Northern Irish). It seems an odd mistake for a history professor.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Weaver and at least one other person call South Boston "South Boston". Most Massachusetts residents would call it "Southie."
Goof (errors in geography): Porter says he's sending one group of people to Marblehead and another along Route 3 to Revere in order to scatter them from skitter aerial recon. Revere is on the way to Marblehead from Boston, and neither US Route 3 nor State Route 3 go anywhere near Revere.
Goof (errors in geography): In Acton, MA, the war memorial says "1914-1918" and "1939-1945". That's correct for a Canadian war memorial, but an American one would read "1917-1918" and "1941-1945".
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Tom Mason uses historical examples of battles. He refers to the Battle of Stirling Bridge (1297) as the Scottish against the British. It was actually the Scottish and against the English - the formation of Great Britain and the cultural identity of being 'British' only existed from the 18th Century. The character is actually a history professor so shouldn't make this sort of mistake.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Colonel Porter wears the flag on the wrong sleeve of his uniform. It's supposed to be worn on the right sleeve, but he is seen in multiple episodes wearing it on his left.
Goof (revealing mistake): SPOILER: In the final shot of the episode, automobile traffic is visible moving in the background.
Goof (continuity error): The heroin, that Tom and Anne are inspecting, continuously changes packaging while they are looking at it. This happens throughout the entirety of the scene.
Goof (continuity error): When the guards from the lodge are walking the 2nd Massachusetts kids' security team away, they pass a lone tree and approach a pickup truck. The camera cuts to Ben, who is watching from the soccer field. Several seconds later, the camera returns to the men walking away, and they are again passing the same tree.
Goof (factual errors): When the RPG is used to shot down the alien craft it had its case remade in alien metal. RPG is a shaped charge weapon, on impact there is a flame that cuts through the metal, hence the case material is irrelevant.
Goof (continuity error): When the two skitters are killed, the shooters blow the heads off in front of Matt. However, there is no 'blood void' behind him where his body would prevent it from hitting the wall.
Goof (continuity error): Towards the end of the episode when Lourdes, Tom and Dr. Glass are in the hospital room with Captain Weaver, when Weaver first wakes up, Dr. Glass and Tom rush to his bedside to talk to him. Cut to wide shot of the room and all of a sudden, Jamil is at his bedside in between Dr. Glass and Tom. Guy comes to hospital door to tell Tom that Pope wants to talk to him, there would've been no time for Jamil to leave the room, but when it shows a wide shot of the room again, Jamil is nowhere to be seen.