I love a good puzzle.

Some of my favorite kinds are strictly conceptual, meaning that once created, these objects require you to simply look and think about them. You can hold them, shake them, examine them . . . but you can't physically disassemble the completed object.

I have several such items at my house that just sit on a shelf and cause visitors to scratch their heads and say ". . . wait . . . how did you . . ?"

Spoiler Alert:

In this instructable, I'm showing how I put two standard tennis balls into a completely unaltered bottle.

For any readers that enjoy puzzles and are up for a challenge: stop reading, examine the photo above, and try to duplicate it on your own. To you brave souls, I bid you good luck and happy problem-solving; come back when you've got it and let me know how it went!

For everyone else, read on to see how I did this.

Step 1: Bottle and Balls

The bottle I'm using is a carafe I got at a local thrift store for 50 cents. The narrowest internal part of the neck is about 1 5/8" (4.1 cm) in diameter.

The balls are standard tennis balls and are about 2 5/8" (6.6 cm) in diameter.

Step 2: Considerations

I encountered some funny things as a result of the fact that I used generic Walmart tennis balls for this.

From whatever manufacturing process is used to make these tennis balls, they're left with these little flaps on the rubber seams which distract people into thinking something is amiss where there really isn't. Also, the lack of any branding or logos leads people to think these tennis balls are "trick balls" or something, which they are not.

Because of this, I recommend using higher quality tennis balls for the sake of presentation. Whatever tennis balls you use will work exactly the same, however.

Step 3: Cut

Use a sharp hobby knife to make a 1/4" incision in each ball.

Note that when you press the ball a certain way it opens up. When you release, the cut disappears.

Step 4: Fold

On the opposite side of the ball from the incision, press that half of the ball inward to create a bowl shape.

Then fold the ball in half as shown. It's critical that the cut be facing outward at this point.

This may take some effort and ninja-like grip strength.

Step 5: Wedge

The ball is now wedged into the bottle.

Compress the ball as much as possible before you begin to wedge it in. With a moderate amount of pressure the ball should plop down into the bottle.

If you're concerned that the bottle neck may break from the outward pressure of the compressed ball, you might want to wear gloves, long sleeves, and goggles. (I did not do this, but the thought certainly crossed my mind.)

Step 6: Wait

Because the cut is on the outside of the folded ball, it is being somewhat held open which allows air to return into the ball.

If you wait a few seconds the ball will re-inflate by itself.

If it does not, you can prod it a little with a long dowel until it does.

Step 7: Fluff

If upon close inspection the incision is visible, use a long wire with a bend on the end to fluff up the fibers around the cut to mask it.

This little implement was made from a straightened piece of wire with a couple of L bends on either end.

It is useful for many things.

Now just repeat the process for the second tennis ball.

Step 8: Done!

That's it!

It's seems simple and obvious . . . once you've seen how it was done. Can you think of another way you could do this, perhaps with a bottle with a smaller neck?

If you're up for a tougher challenge, check out my Deck of Cards in a Bottle instructable.

Thanks for reading!

Update: I eventually donated this to a local thrift store, and was amused when I saw the price they put on it: $1.50