Joan smiles at Ted, then leans against him, resting her head on his shoulder, and watches their friends as well. They're definitely different sorts of people, with Beard being generally quiet while Sherlock is frequently loud and brash and rude. And yet this silent moment of staring demonstrates at least one of their similarities...a dislike of small talk and a lack of care about social convention that dictate what friendly interaction looks like.

Joan is not a very talkative person in general, so she's happy to let them have this moment of silence, while she is also aware it is quite likely that Ted will be the first to break the silence.