In Somewhere, when Cleo and her father are under the water in the swimming pool, what are they pretending to be doing? It seems to me they pretend to be eating something.
They're having an underwater tea party. An imaginary tea party is a common playtime acivity among kids; Johnny and Cleo are simply having it in a pool. Says Stephen Dorff who plays Johnny (about the Chateau Marmont hotel):
When you stay in a hotel for that long, and you have friends come join you, you kind of host the party every night, so I'm paying for everything — and ... it can add up every time you have a coffee. It was a good lesson to learn. I then ultimately had my 21st-birthday party there, which ended in a big ... synchronized-swimming party in the pool, which ultimately [in Somewhere] I do my underwater tea party with [onscreen daughter] Elle Fanning in, so there's been all these moments there."
Here, for example, is Cleo when she mimes sipping from a pretend tea cup: