The Puzzle Knife
The first half of the 17th century saw an increase in the use of folding knives, including the invention of the "puzzle knife". The blade was locked shut with a pair of large rivets. Each puzzle knife had its own individual (though often similar) way of opening the blade.
Later, more refined knives (like that shown in the image), featured a series of dials that served basically as combination locks for opening the blade.
For more info on similar puzzles, Jerry Slocum with Indiana University has published a list of early mechanical puzzles dating from the 10th Century B.C. to the 19th Century. The PDF can be downloaded at:http://www.indiana.edu/~liblilly/collections/overview/puzzle_docs/early_puzzles-dartmouth.pdf#puzzle #mechanical #knife #spanish