Impossible Bottle (Harry Eng)

I know they aren't mechanical puzzles in the strictest sense, but I really do love impossible objects. I like to ponder over how they have been created, but strangely I don't really want to know the answers as I'd much rather keep on guessing.

Harry Eng is widely regarded as being the master of the 'impossible bottles'. Over the 64 years of his life Harry put decks of cards, tennis balls, tools and even shoes into glass bottles. A particular signature of his was being able to tie complete and complex knots inside bottles as well!

I was very lucky as to stumble across this particular bottle on eBay of all places! 

It was used as an exchange puzzle in Seattle in 1994 for IPP14. It is just a standard glass bottle containing a full monkey's fist knot loose in the bottom, with a whole tennis ball above it. The neck of the bottle is obviously too small for either of these two items to be in there, and yet there they are.

In case you were curious, yes I did check to see if the tennis ball was fully inflated by prodding it with a pen, and it is. I can only guess how this very curious object was created, but like I said, I don't really want to know the answer. I much prefer to pose the question to others instead and see what kind of amazing and elaborate ideas they come up with.

Keep an eye out for some of these creations if you find them as interesting as I do. Or as an even better suggestion, have a try at making one yourself! I mean how hard could it be right?