yap
afrer velie go to troop -> on grownd folow to near cave anter -> there is plant - use it

Where do you get the shell again? I played the game twice to get some achivements, but I skipped the cutscenes sometimes.

At the bottom left of Tropos, on the solid ground, there's a patch of dirt that can be examined. If the owl kid has the seashell, he'll take it out and listen for a moment. …And if the mechanic guy is in the party at the moment, he'll pop in for a talk.
(This gives you an achievement.)