The Politico:

I was still kind of amused by her brief interaction with Mitt Romney in the press file just now.
[Senator] McCaskill was stepping out of her chair at the end of an MSNBC interview, and Romney was up next. She and a staffer unplugged her various wires, and she handed Romney the earpiece the guests use to hear the host.
“I spit on this before I put it in,” she said to Romney, with a sweet smile.
UPDATE: Romney spokesman Eric Fehrnstrom emails: “You should have seen what she did to the chair.”