Other mistake: When the Doctor gets George's psychic cry for help, he's shown reading the message without opening the wallet containing the psychic paper. This despite the fact that all previous instances of the Doctor receiving psychic messages this way has required him to open the wallet, suggesting that the wallet itself does not display the message. (00:02:02)
Continuity mistake: When Amy and Rory are searching the darkened kitchen, the flashlight Rory holds switches hands between cuts when it starts turning on and off. (00:13:52)
Continuity mistake: When Purcell is sinking into his carpet, just after a shot where he's shown having sunk into the floor up to his waist, we see a shot focusing on his dog where Purcell's legs are visible as he falls forward onto his hands, despite his legs having already been pulled under. (00:23:38)
Continuity mistake: When Alex is hugging George after rescuing him from the peg dolls, George's arms are down in shots facing Alex, but his left arm is up in shots facing him. (00:37:23)
Revealing mistake: When the landlord, Purcell, wakes up on his floor because his pet dog is licking his hand, we see a few pieces of dog food fall from his fingers - should have been a re-shoot, but all credit to the actor, he knows it has happened and is quick to hide them again. (00:38:38)
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.