Bonsai Kitten discussed stuffing cute lil' kittycat into a Klein jar. Klein jars can only exist where there are four spatial dimensions, which wherever it is ain't here. That mention was their disclaimer, their ;-), their </sarcasm>, their "kids don't do this at home."
I suppose some folks have actually never heard of Klein jars. But in defense of the guys who made the site, having as they do that odd world view peculiar to MIT students (calm down Carl), it's certain they assumed that everyone in the world older than about ten knew it. There's a photo of a glass fake Klein jar in the Time-Life Science series volume "Mathematics," which I got, inscribed "Learn damn it - love Dad," thirty five years ago.
Yours WDK - WKiernan at concentric.net