Interesting, I did very badly, 3/10!

3/10 too, and I've actually tried to discern the answer. My working theory was to pick texts which jumped between more to less frequent words (subjectively of course), but I was very wrong, basically I couldn't spot a watermarked trait at all.

Same, doing worse than random chance seems like an interesting signal though, but I'm not sure what it's a signal of.

Only one third of the options at each stage are watermarked, so 3/10 seems well within random chance.