Espressivo e Tranquillo

I was talking terms with a 10-yr-old today (in Seitz's Concerto No. 2, Third Movement, for those of you playing at home).

Me: What does espressivo e tranquillo mean?
Girl: Oh.  We talked about this last week....
Me: Espressivo...?
Girl: Oh!  Um.. sounds like... Expressive!
Me: Yes!  [very pleased that she didn't say 'espresso' like last week].  E?
Girl: And!
Me: Yes! Tranquillo?
Girl: Nnnnnno idea. [I start miming, like I'm smoothing something].  Oh, flat? boring?
Me: Chop the -lo and you get the word tranquil.  Do you know what that means? [girl shakes head]. Calm... peaceful... like a calm lake.  So how are you going to play expressively? [girl shrugs].  Keep using that lovely vibrato [hers is coming along beautifully] and lots of dynamics.
Girl: But how can you play expressively and calmly?

I played the passage expressively and agitato, then again expressively but with far less accentuation from the bow.

Girl: Oh yeah!  It does sound like a lake!