In the scene towards the end where Clara falls into The Doctors arms, the side to which she falls changes between front and rear shots.
When Clara sees the Fifth Doctor trapped in the Matrix, the ring on her left hand switches to her right between shots.
When Clara passes out in the Doctor's time stream and the Doctor catches her, he lifts her up so that her right arm is holding onto his left shoulder. When the shot changes, her right arm is suddenly swinging loose by her side and holding onto her leaf.
When Clara passes out to join the "conference call," she falls forward. When she is shown waking up, she is lying on her back.
At the beginning, the Time Lord mechanic says, "What kind of idiot would try and steal a faulty TARDIS?" It was not the Time Lords who invented the name TARDIS. It was the Doctor's granddaughter Susan who invented the name out of the initials "Time And Relative Dimension In Space". Even the Doctor did not call it the TARDIS at this point. The Time Lords did not call it a TARDIS until 1969.
When Clara passes out at the end, the Doctor carries her in his arms. But Clara, who's meant to be unconscious, is still holding the leaf. When she wouldn't be able to hold onto the leaf if she wasn't conscious as your body is relaxed when you're not awake.
When Vastra is yelling at Strax after the Great Intelligence has rewritten the Doctor's life and removed their friendship from history, Neve McIntosh's natural Scottish accent can be heard slipping through.
The body double for the Second Doctor who runs past Clara has a dark color wig, resembling the Second Doctor's appearance during his tenure as the star of the show. However, the archival footage it is mixed in with (the Doctor running while wearing a fur coat) was taken from his return in "The Five Doctors," by which point Patrick Troughton's hair was visibly graying.
The Great Intelligence has many of the "shadow men" at his command, yet only 4 are ever seen on screen at once. Even when there are more than 4 in a scene, they are the same 4 filmed from different angles.
After the Great Intelligence has entered his time stream and the Doctor begins dying all at once across his life, when he is thrashing around on the ground, he is heard screaming even when his mouth is closed.
After River's projection says she was the one to open the door, she walks to the right hand side. At this point no one except Clara can see her, however although he is out of focus, you can see Dr Simeon's eye-line follow her as she disappears off camera.