When Rex is on the plane ready to take-off for the U.K. a right hand is shown reaching over to grab the phone and disconnect the call, the wrist has no watch. Yet when Rex recalls the sequence later after he sees Captain Jack Harkness save Gwen, Rhys and him - we see a left hand with Jack's leather cuff (his vortex manipulator) clearly visible. And if the 'right hand' had been Jack's we would have seen his wristwatch as he wears it on his right wrist.
When Danes is talking to the Governor's representative, there is no sign on his arm of the IV insertion that was used in his failed execution. There would be some bruising, at the least.
Rex is impaled by a spike that comes from the back of the lorry in front of him when it stops suddenly. The spike should have continued to try and move in the direction of the vehicle rather than changing its direction of motion by 180 degrees.
Even if no one dies, a population explosion beyond the planet's resources would take years, not months, to happen. In that time the number of births could be reduced, and thus the population would level out.
The helicopter explodes only a few feet from Gwen, yet her hair doesn't even move although there must have been a shock wave.