After the survivors get across the bridge they go into a side room to re-chrge Bannakafalata's EMP and they know each other well but as they enter the room the Doctor tells mr Copper to bandage hs cut but he said "Who are you...Mr Copper."he should have said "Mr Copper".

There are 2 possibilitys:1)David Tennant forgot who was playing Mr Copper or 2)It was the first day of filming and David didn't know who he was.

I can't belive no one noticed.