[Nami's face goes through a range of expressions as Law speaks-- from hopeful to slightly confused yet understanding, worry, a faint cringe at the talk of parasites, and finally a faint and measuring look as she considers that last part.]

Katara might be able to help. She's dealt with...things wrong that aren't visible before this. [She might not be able to detect a mushi, but then again there's no harm in checking.]

I haven't discussed this with Sayo yet. I didn't want to get her hopes up.