Clara's hair pin changes sides during the last scene inside the TARDIS.
At about 7:30, as The Doctor and Clara are standing in the narrow corridor talking, The Doctor is standing facing directly down the corridor. When the camera is over his shoulder, though, he's standing at an angle with his head turned towards Clara.
When Clara is in the darkened coach talking to The Doctor on her cell phone, the phone's screen is on and lights up the side of her face. Smartphones have a sensor that blanks out the screen when held to one's ear and talking on them so that one doesn't accidentally dial or activate some other button that touches the cheek.
On more than one occasion, Perkins starts "the clock" several seconds after the mummy has appeared, so the mummy kills its victims in a longer time than the 66 seconds as suggested.