#because the original hand was a special-effect-guy's hand and it didn't look like david's hand

[mizgnomer]

Behind the Scene of Turn Left (Part 2)

Excerpt from DWM 397′s feature on Turn Left, by Jason Arnopp:

Why doesn’t the Doctor regenerate when he dies in Turn Left?

Russell T. Davies (writer/showrunner): “Well, you won’t have seen this in the script,” he reveals, “but there’ll actually be an ADR line added to that effect. Notice that Private Harris is out of vision when he says, 'Must have happened too fast for him to regenerate.’ cos that line will be added! It’s fascinating, that, cos I think some new viewers of Doctor Who assume that regeneration means that the Doctor can never die. But that’s never been the case! If he’s dead, he’s dead. Bullet to the head, flattened by concrete, thrown into a compost machine, no more Doctor. It’s only if he’s dying that he stands a chance. I think, as a long term fan, I’d taken that so much for granted that I forgot to say so in Turn Left.  It was only when I was watching the final, online edit of the show, that it clicked - some kids might be expecting a regenerative glow, underneath those ambulance blankets!  So right at the very last minute, we got the actor, Clive Standen, to add that line. I imagine, by the way, that the Doctor died because half the Thames Flood Barrier fell on his head. It’s not pretty, under those blankets. But then, when is it?

Also, David Tennant from Doctor Who Confidential:

I just want to know who played my hand in the scene with the stretcher.  Because it wasn’t me.  I read it in the script but I never got called on set.  I’m gonna study that hand, and if it doesn’t look exactly like that hand [ holding his hand up ], I’m gonna have words.

(Note:  The deceased Tenth Doctor on the stretcher was played by Colum Sanson-Regan, David’s stand-in on Doctor Who

Bonus:

Link to [ Part One ] (or click the #whoBtsTurnLeft tag)