When Lucy, Viv and Joan toast with their lemonade and Lucy's goblet shatters, the stem of Joan's cup also breaks off. Joan momentarily has no way to set down the full cup of lemonade as the scene blacks out.
When Joan is headed out of the room to get the lemonade for Lucy and Viv, a small white object can be seen moving through the doorway off stage. This is a backstage assistant ready to hand the camp stool props to Crawford for her next entrance.