Don't overlook this little trick!
Many tanglement puzzles like the one in the first picture can be assembled a second way, which can pose an unexpected challenge. After disassembling, turn one piece around and reassemble with one piece flipped.
For example, here's how people ordinarily assemble the Bent Nails
puzzle by sliding the two points into the loop of the other piece:
File comment: Ordinary method of assembling by moving each point through the loop of the other piece.
IMG_4645.JPG [ 192.76 KiB | Viewed 1305 times ]
Instead of the standard method turn one piece around like this
so the point of one piece is going through a loop, and the nailhead of the other piece is going through a loop:
File comment: Alternate method, turn one piece around so its head is moving through the loop.
IMG_4646.JPG [ 192.67 KiB | Viewed 1305 times ]
After assembling the puzzle this unusual way set it down and take your hands off it. Then pick it up and try to disassemble it normally. You'll probably be surprised!
This is a surprisingly effective (but harmless) prank to pull on someone who's memorized the solution to one of these puzzles, especially if they don't see you flip the piece. The better they 'know' the solution, the harder they'll find it to solve!