My buddy Jon makes these awesome little puzzle boxes from acorns. There are four shown in the video: one pair consisting of a smaller hinged acorn that nests, matryoshka-style, inside a larger one with a wire spring latch; a larger, locking nut that is opened by removing a small pin; and, finally, a large hinged version that is unlatched by knocking it against a surface from a certain angle. Besides this post, the project doesn’t have any web presence to speak of, but Jon says its fine to e-mail him directly if you are interested in more information.