I just ordered one of these recently! Last week, I finished reading "The Cuckoo's Egg,"[0] about a computer espionage case in the late 1980s (great book, by the way.) Afterwards, I was looking up the author's information, and found the klein bottle website, and videos with Numberphile.
Cliff actually sent photos of the klein bottle I ordered as it was being packaged up for shipping! Lots of humorous tidbits hidden all around the website. Worth taking a few minutes to explore around.