Older guys will remember these toys but I've not seen them in the stores lately. Very simple toy - blow through the pipe and the string whizzes round forming a nice loop. Prints without support. Thread a length of knitting yarn (wool) through the pipe after printing, and form it into a loop by splicing the ends together. If you're not very good at splicing (like me) a trace of superglue makes a good join. A knot would (probably) be too big to pass smoothly through the pipe.