Continuity mistake: When Andy gets sprayed with blood at the virus outbreak scene, when a sniper saves his life the blood splatter changes several times over the movie. (00:54:15)
Continuity mistake: Don attacks a man in the underground carpark and thumbs out his eyes as he did with his wife. The man gets up in the next shot perfectly OK.
Continuity mistake: When the plane lands at the airport, it is a Boeing 737 without winglets. When it taxis to the apron in the next shot, it is a Boeing 757. Then again it is a 737 with winglets, then without and finally with them.
Continuity mistake: After Don escapes from the house at the beginning of the film, the infected are right behind him. He manages to escape in the boat but when the following shots show the river, there is no sign of any bodies or blood (despite one infected being killed by the boats propeller) or any disturbances on the surface apart from waves being caused by the boat. There is no chance that the infected could have all gotten out of the river so quick (including the dead infected body) without leaving so much as a splash. (00:10:35)
Answer: Nobody ever said they could only come out at night. As their food became scarce, they'd taken to daylight hunting as well.
Captain Defenestrator