When Castle is first looking at the neighbors with the binoculars, he sees a man talking to a woman with a laptop and says, "Hmm, must be writers." The man and woman appear to be creator/writer Andrew W. Marlowe and writer Terri Edda Miller.
At the very last scene, Castle asks Becket how many murders they've solved since they met and she replies "Maybe a hundred or so". This episode marks the 100th episode of the show.
When the title appears, the blood/ink from the pen spells out the number "100". This happens to be the 100th show.
Pays homage to another Alfred Hitchcock movie, Rebecca (1940). In that movie, there is a character named Mrs. de Winter.