Continuity mistake: At the very end of the episode, when Rex is checking his phone, when the camera is facing him, his phone is being held in portrait, but when the camera is over his shoulder, looking at the screen, the phone is in landscape. This is shown twice, when the camera shots switch.
Continuity mistake: Gwen views a transparency of two Torchwood members from 1918. The words "Torchwood" can be seen behind them. When Ianto takes the transparency and holds it up, the slide is different: it contains five people and the word "Torchwood" is above their heads.