When Rose is answering the last question in the Ann-Droid game, the score tally shows the question marked as wrong before she actually answers.
When the guard first holds up the sonic screwdriver asking what it is, the colored cover is missing.
Just after The Doctor, Jack and Lynda break out of the prison cell, Lynda reaches for her gadgets twice.
When The Doctor, Lynda and Strood sit down to watch Crosbie on the TV screen, the Doctor puts his hands behind his head, but when the camera is behind them, his arms are crossed, then when it switches back to in front of them, his arms are behind him again.
As the Doctor, Captain Jack and Lynda with a Y have been captured, the Doctor turns his head to the right, then after it cuts it shows him turning his head again and saying "Lets Do It".
Just before the Doctor remembers what happened to him, behind him and Lynda a crew member can be seen running past.
The Doctor concludes that the contestants in the various games on The Station are not being killed but in fact teleported to a slave chamber by the Daleks. However Captain Jack is very much nearly killed by a chainsaw wielding robot in his chamber, so clearly at least some contestants are actually being murdered.
The Doctor claims the Daleks are hiding themselves from sonar. But sonar relies on sound waves, which can't travel through the vacuum of space.