[Sokka really isn't underestimating Snivy, but he's not one to kowtow to anyone (or anything) just to win its love. He's sure Snivy is totally capable, but he's not going to admit it.

Sokka takes the Poké ball and holds it closely, inspecting it with a deep focus for a few moments.]

Well, yeah, I can see why it doesn't work, obviously. Though it looks like it's made of just ordinary metal... but... not metal. It's definitely... something that I haven't seen before.