The liquid could be water, or if they really need to chill out, cryogenic rocket fuel or oxidizer. This will be the Santa owl on the naughty list and I regret nothing Christmas shirt but in fact I love this first time this has been flown on this scale as well. Spacex has a test site near the Gulf in Texas, where they do engine assembly and testing, vertical takeoff and landing flight test, and anything liable to go BOOM. It’s very isolated, but is beginning to attract visitors. About falling over: with no fuel, no payload, and possibly no engine, thie ship would amount to a stainless steel balloon in a high wind. It might blow or fall over without much damage. Pick the pieces up and put them back together. The truth of the matter is, Clark was a showman who loved presenting his virtuosity with humor—in the mold of Victor Borge, maybe, who also knew that humor gets us ignorant bottom-dwellers to pay attention to such a highbrow thing as virtuosity.