Visible crew/equipment: After John acts out what the word "shoot" means before he and Aeryn release the vorc, it cuts to the wiggly-eared vorc moving down a corridor while Aeryn and John follow behind him, and we can see a crew member's arm holding cables for the moving animatronic vorc, at the left side of the screen.
Visible crew/equipment: After Aeryn and John kill the parasitic Rygel and hundreds of little parasites, it cuts to the medlab where Rygel is explaining to D'Argo and Chiana what happened to him, and we can see the puppeteer's head behind Rygel. As an aside, earlier when Aeryn grabs parasitic Rygel off Zhaan and throws him, note that Zhaan's arm is under Rygel's robe to control his movements.
Chosen answer: It's never explained. John mentions a theory that his less technologically developed craft simply interferes with the wormhole less than the "superior" Vipers, but they never make a concrete determination on that point. But we also have to take into account the fact that Moya traverses wormholes with no ill effect as well.
Garlonuss ★