Boo's mouth was slightly opened in this shot like he was getting ready to talk about his water situation. He and Luna have a new water fountain, but Boo insists on sitting in the prep sink and drinking from the tap while socializing with the family. The instructions are not to turn the prep sink tap on so that Boo will go to his new water fountain. Boo being the social, smart, stubborn cat that he is may win this battle and remain a tap drinker. Luna is using the new water fountain.
Ian