[Brax's hearts sink a little at this news but takes it in stride as he doesn't doubt the Doctor expects him to do.]

Understood. Try not to get into mischief, Thete.

['Thete'. The only sign he's worried about him, the childish nickname that he only used on the Christmas presents and never out loud; the full stop signalling that he doesn't expect a reply; both belying the chiding nature of the words themselves which only grants the Doctor the luxury of ignoring sentiment.]