Speaking of the Necker Cube and gender stuff, I want ti highlight what's the oldest attested example of this online, now only available via the internet archive (CW for frank discussion of slurs, and also outdated terminology, because it's from 1996):
http://web.archive.org/web/19990508025838/http://www.chaparraltree.com:80/raq/
There's so much awesome stuff here; it also includes the oldest example I can find of the Gender Diamond diagram which I came up with independently like 10 years later, thinking I was being terribly original, and also this is what got me reading Bone Dance, a novel that hits on so many of my personal meaning buttons that it's baffling and frustrating that I didn't read it until 2013 or so.
@indi I ran across it in '99, and still managed to get my head tied up in a knot for a long time because... brains are like that?