Real crowd pleaser, pops out with a fun little noise. Considered a puzzle but I usually just show people what it's about before handing it to them. http://youtu.be/8RUr8m1OZLI . One version is like in the video, with or without magnet holes*. The flat version is something I saw here, and it's also cool: http://www.grand-illusions.com/acatalog/Raketti.html . * The magnet holes are for cylindrical neodymium magnets, 3x5mm in part A and 3x3mm in part B. Any less, and part A still pops out if you blow hard right into the gap. I'm not a huge fan of the magnet trick, but you might as well do it right if you do it. For magnets, I recommend ordering 3x1mm pieces and stacking them as needed (on dx they're like $4 for 100). Or just order some 3x3 and 3x5 pieces, they're more fun. In any case, I would leave a bit of space in the hole and top it off with something, maybe the same glue I use for the magnet, because I've had issues with magnets coming loose (also make sure to wipe the magnets clean of any oils before gluing).