Eric Hart had a deceptively simple sounding project pop into his lap.
We built a doll that moves its arms, dips a wand into soap, and brings it to her mouth to blow bubbles. It was for a theater production, so one of the challenges was for it to run smoothly every night with just a push of a button. It was particularly difficult to make the bubbles behave consistently. If I were to build one again, I would start by solidifying the mechanical parts first and then crafting the visual portion around it; in this case, we built the doll parts first and then had to make the mechanics fit that, which limited our options as we discovered problems with the design.
As you can see, he managed to pull it off nicely.
His blog has the full build details and many pictures of the process.