Henry: *shrieks* No! Flynn goes ba-booo! (That's the noise that Icelandic fire sirens make)
Ross: Yeah, usually, okay, but maybe he doesn't have the siren on... Fire trucks have engines, so they still make a *vroom* sound while they're driving. It's not an emergency, so he's not using the siren, see? So that means we can hear the engine going *vroooo-
Henry: BAAAAAAAA. BOOOOOOO.