After the costume chat two days ago (probably worth reading the Costumes post for context), it seems as though something got through to Sam. Kind of...
Getting out of the bath:
Sammy: Mum, I just want to be myself today.
Mum: That's nice.
Sammy: No spies, no ninjas, no Batman. Just me.
Sam walks out the bathroom humming.
Mum: I think that's lovely. It'll be great to spend the day with my Sammy.
Sammy: Sammy? I'm not Sammy I'm George the Mouse. Just George. Me.