Amy's hair changes through the story.
A human heart in asystole (flatline) cannot be restarted by a defibrillator. The treatment is CPR.
The cubes are meant to be completely identical and with 'no flaws' to their perfect cubic nature whatever. Just after the soldier's enter, the doctor picks up a cube and plays about with it, tossing it and turning it over in his hands. At the last moment of the shot, a dent and a line, possibly from tape meant to keep the cube together, can clearly be seen at the top of one of the cubes.
When The Doctor vacuums the living room and Amy lifts her legs up in the sofa, you can clearly see the microphone transmitter in her back trouser pocket.