McCaskill's edge

I mentioned a few days ago that Missouri Senator Claire McCaskill's mild affect masks a bit of a killer, and that she's perhaps the Obama campaign's deftest surrogate on the attack.

But I was still kind of amused by her brief interaction with Mitt Romney in the press file just now.

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."

UPDATE: McCaskill spokeswoman Maria Speiser says the exchange began when Romney said, "You don't have an ear infection, do you?" and that McCaskill was joking back in response.