So thank you Moffat, thank you for allowing the guilt and pain and memories to resurface. As an incredibly nostalgic person, I really do appreciate it.
Also, I quite enjoyed explaining away River's lack of regeneration in Forest of the Dead, and am intrigued as to what this question is. Could it be the same question that we're trying to figure out about Life, the Universe, and Everything? Because if so, I know the answer.