Because of the way they're interlinked, it's impossible to make Borromean rings out of true rings. But Lilli's teething rings are actually ellipsoid, so I was able to get away with it. I still can't lay them completely flat, though (top).
 She hasn't started teething, yet, but she still likes to play with them.
 See http://en.wikipedia.org/wiki/Borromean rings for a more in-depth treatment.
 See http://en.wikipedia.org/wiki/Borromean rings#History.
Borromean Rings is by Jim.belk, available at http://en.wikipedia.org/wiki/File:Borromean Rings Illusion.png.