Continuity mistake: When the Doctor and Nardole are being held by the Picts in a circle of weapons being pointed at them, when Kar's brother points a knife at the Doctor and warns him not to speak until she gets back, his arm is almost fully extended in shots from above and facing the Doctor, but much more bent in shots facing him. (00:12:40)
Continuity mistake: After Nardole gets Pictish facepaint, the lines change in consistency and exact positioning several times throughout the episode.
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.