when Melody asked who River is, the Doctor says "Spoilers" because he's remembering all those other times he met River. all those times she says "spoilers" she's quoting him, and all those times he says "spoilers" he's quoting her
John Barrowman Knows The Difference Between Nerds and Everyone Else
And the fact that he ignored the glass case it was in. I'll bet he put a fez on his Christmas list along with a Stetson. This is beautiful. This is one of the reasons why Matt Smith was and is the best Doctor.