View Full Version : Impossible Object Puzzle Solution?

02-01-2005, 01:07 PM
A student of mine, hell-bent to drive me nuts, handed me a puzzle this morning. It's called a Tooth and Nail puzzle and looks like this:


The goal of the puzzle is to remove the nail without destroying the puzzle. The student claims that the nail can be freed and returned to the block with only 5 seconds of work.
It seems to be cut out of a single piece of wood and the nail appears to be an ordinary wood nail. The nail can slide back and forth through the holes in the wood "teeth", but the extent of the motion is limited by the end "teeth".

Any ideas on a solution and/or how it was made? (an hour's worth of Googling came up with nothing...)

My take: there's no real solution for physically removing it. It's an optical illusion-type puzzle. If you stare at it long enough, just right (ala the "floating finger" trick), it appears that the wood teeth dissapear and the nail is "free". Moving the block out of this focal plane causes the nail to "return" to the block. Or, maybe it's the pain killers I'm on that making this solution possible...

If this "solution" is correct, it still doesn't reveal how it was constructed.

There's some discussion on various fora that these are made my boiling the cut wood to make it pliable enough to be bent open in a clamp, allowing the hole to be drilled and the nail inserted. Others claim this isn't so.

02-01-2005, 01:14 PM
Or, maybe it's the pain killers I'm on that's making this solution possible...

again, damn painkillers.... :p
(or...damn the grammar, I'm a science teacher, not an English teacher!)

Gary Robson
02-01-2005, 01:43 PM
It's hard to tell from the picture, stochastic, but would the head of the nail happen to be only slightly larger than the holes in the wood? If so, maybe it's a coefficient of expansion thing -- get it very cold and the metal of the nail shrinks enough to fit through the hole (wood expands and contracts a lot with humidity, but not much with temperature).

02-01-2005, 02:00 PM
I think this is one of those "gee-wizz!" items. Not so much a puzzle as simply puzzling. Like those "Arrow Through a Heart" items. This is just a theory, but I've always assumed that the "through" object (the arrow or in this case, the nail) is inserted into or through the other item, and then one is allowed to grow around the other. That's why one of the objects is always wood - usually softwood as it grows faster. Place the coin with a hole in the center over the tree branch, let it grow (the branch), and then carve the branch into an arrow.

In this case, perhaps the nail was inserted into the wood when it was young. Okay, okay - looking closer that seems pretty improbable. But that's my best guess.

In any case, I wouldn't bother trying to solve it - I don't think the nail is intended to be removable.

Terminus Est
02-01-2005, 02:07 PM
You're not supposed to take the nail out. From the Impossible Objects home (http://www.johnrausch.com/PuzzleWorld/toc.asp?t=_cat/io001.htm&m=cat/io000.htm):
Is it a puzzle or is it a magic trick? Impossible objects are difficult to classify. They really aren't mechanical because they don't move (usually) and you don't manipulate any of their parts to solve them. You just look at them and think. And they aren't really a magic trick. There's no performer, at least not when you're dealing with the object. But they have the same "how did they do that" quality that a magic trick has. The puzzle is to figure out how they were made.
[bolding mine]

02-01-2005, 02:08 PM
The usual solution for the arrow puzzle is to squeeze the head in a vise until it's small enought to pass through the hole. Here you might be able to flatten the end tooth enough to free the nail. (I seem to recall soaking as one step, but that might just be to make the wood return to its original shape.)

02-01-2005, 02:12 PM
rjk has it. The puzzle is discussed here (http://www.answers.google.com/answers/threadview?id=344364) and the solution posted at the bottom describes the process in a little more detail.

02-01-2005, 03:25 PM
I saw an episode of "woodwright's shop" that showed how to make the nail in the comb thing.

spoiler, just in case

Soak the comb in water. squeeze the tine at the nail head end in a vise.
Allow the comb to dry (still in vise)
Then drill holes in the tines (the end tine will be compessed enough to not get drilled)
put the nail in and soak the comb in water again. The end tine will re-expand.


02-01-2005, 04:36 PM
Thanks, folks, for the replies and links! I think I can sleep tonight and not toss and turn, wondering how this was done. Now, I want to make one for myself! I can toss it to the ADHD kids in my classes when they get too fidgety to keep them busy.

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