Joan can't help a small smile as well at Beard's perfect reaction. This is why she trusts him.

"Sherlock," she says. Which is probably obvious. "But that's it. Everyone else needs to believe that we've broken up." She squeezes Ted's hand. "I have a plane to New York tonight. I'd like you to come with me to get my bags at 221B. I'm going to give you a burner phone that you can inconspicuously pass on to Ted so we can communicate."