"I'm gonna have to play other people if I ever want a chance of beating you." River makes sure her apprentices get their share ("Take lunch, we're kicking our own asses here.") and leads Annabel into the kitchen where -

"Aaaand I left the chess manual I checked out from the library on the table," River notes. Her voice is flat but her face is mortified. "It's fine. It's all fine. I'll just jump into my forge now."