It is raining and Gwen is sitting inside the car. PC Andy gets in complaining about how he "walked... [he] bloody walked" yet he is completely dry.
When describing how the "invisible lift" works Jack says: "If I were to guess, l'd say that there was once a dimensionally transcendental chameleon-circuit placed right on this spot, which welded its perception properties to spatio-temporal rift." Whilst he is very clearly talking about the Tardis which landed there in Boom Town (2005) in actuality the Tardis landed a few feet in front of where the lift is located as the lift is above the sidewalk edge and the Tardis landed on the pavement below.
The level of beer in Gwen's glass when she is in the bar with Jack changes between shots.
As Torchwood resurrects John Tucker, it is raining in Cardiff, soaking everybody outside, including Gwen. When she returns home to her flat in the next scene, both Gwen and her umbrella appear to be completely dry.
When the Weevil bites the hospital porter's neck, the blood that spurts out isn't remotely the color or consistency of human blood.
Although Captain Jack Harkness is American, he pronounces estrogen in the British manner. He pronounces it as "eestrogen," rather than "ehstrogen," as most Americans do. However, Jack has lived in Britain long enough to pick up British pronunciation of words.
About 13:30 minutes in, whilst Gwen Cooper is following the Torchwood Range Rover, Yvonne is giving her background information about Captain Jack Harkness.
Yvonne says Jack was a member of an Eagle Squadron - 133 Sqn - at the height of The Blitz and he disappeared on the night of 21 January 1941.
Although 133 Sqn was a real Eagle Squadron during WWII (manned by American volunteers prior to the USA entering the war after the Japanese attack on Pearl Harbor), the squadron was only formed on 01 August 1941.
However, history in the Whoniverse didn't always happen the same as in the real world, especially when time-distorted super-beings like Jack are involved.
Yvonne says Jack was a member of an Eagle Squadron - 133 Sqn - at the height of The Blitz and he disappeared on the night of 21 January 1941.
Although 133 Sqn was a real Eagle Squadron during WWII (manned by American volunteers prior to the USA entering the war after the Japanese attack on Pearl Harbor), the squadron was only formed on 01 August 1941.
However, history in the Whoniverse didn't always happen the same as in the real world, especially when time-distorted super-beings like Jack are involved.
When Jack stands up after being shot, the blood from his wound has flowed "down" his face (closer to his nose) but when Jack fell his head came to rest at an angle that would have had the blood to flow to the left and slightly closer to the top of his head.
When interrogating the second (male) murder victim, Jack references a previous victim as "he." But later, they say only one man (and two women) were murdered.
There is no 'Captain' rank in the Royal Air Force, The insignia that Jack Harkness bears on his RAF greatcoat is that of a 'Group Captain'.
A Group Captain would never at any period in history be referred to only as 'Captain'. Within the structure of the RAF and on any official level he would always be referred to, and should refer to himself, as either 'Group Captain Harkness' or 'Group Captain Jack Harkness'.