We have seen Changelings become all sort of things. But is that for real?
When a Changeling becomes a rock, it is a rock, or so our eyes, hands, tongues, pickaxes and tricorders tell us. But is that merely what the Changeling wants us to believe? If it really became a rock, it would cease to be a Changeling, after all - and rocks can't transform into Changelings, even if the opposite is true.
Perhaps Laas simply was very good at fooling people into thinking there was fog on the Promenade. Sure, he could "fool" a Klingon stomach into thinking it was punctured and fatally bleeding, but that probably did involve sticking a knife-shaped part of himself into that tummy. Doing the fog might be more of an illusion, the same way we could speculate that being a rock involves just doing a rock shell and then somehow fooling the tricorder into thinking there was no Changeling goo hiding inside.
But the other option is that a Changeling really can turn its goo fully into any type of matter, while its "Changelingness" rests somewhere else (perhaps right next to the missing mass, or to the commbadge that clearly wasn't visible inside the transparent drinking glass when our favorite Changeling was that glass).
I think the former interpretation would put stricter limitations on what a skilled Changeling can do than the latter...
In any case, Odo isn't merely an illusionist. We never got any reason to think the Salt Vampire or the Talosian Kidnapper would be capable of becoming thin as a snake even if it changed its appearance to that of a snake - a small hole would still be too small for it to crawl through. But the Chameloid in TUC really became so lithe that it could wriggle out of an iron shackle. Odo is closer to the latter than the former, but is he really more? Could he be, with more training? There's no telling. Perhaps Laas simply has learned better stage magic, and doesn't really travel at warp but merely hitchhikes on a runabout and then fools its sensors into thinking that the hanging onto is actually formation flying?
Timo Saloniemi