Memorable Moment: Grammar or Spelling Moment on Castle

In "Home is Where the Heart Stops," a first season episode of Castle, Castle, Esposito and Ryan have the following discussion regarding a series of burglaries:

Castle: How do they know what's in the safes? Safes. Is that a word? Is it "saves"? That can't be right.

Esposito: And you write for a living?

Ryan (with emphasis): We've compared the kind of safes that they had. Nothing's been a match.

This type of discussion crops up quite often in scripts. I imagine they begin in the backrooms where writers hunker down and discuss dialog. "Is it safes or saves? Saves? Why would it be saves?"

One can understand Castle's confusion: dwarf becomes dwarves; leaf becomes leaves. But Ryan is right:

It's safes.