Doctor Who: 20 Things You Didn't Know About Blink
18. David Tennant Recorded His Lines All By Himself
Even though David Tennant isn't in Blink very much, he's still on top form, and went to great lengths to give the best performance possible.
To recreate the half-conversation the Doctor has with Sally, Tennant recorded his lines in a room on his own, without having Carey Mulligan to bounce off.
Don't ever say he didn't suffer for his art.
From a scripting standpoint, this conversation was also presented in a rather lonely manner. Moffat wrote the full conversation, removed Sally's lines, and then handed the Doctor's lines to Tennant, believing that this would make his acting feel more authentic.