At first glance, you would think that these tape measures were merely left by some absentminded carpenters. But there's more than meets the eye to these unassuming retractable rulers. They're actually robots, designed to crawl inch by inexorable inch towards the finish line.
Keiko Takahashi built these Meter Crawlers out of off-the-shelf steel tape measures. The robotic internals extend the metal tape, then retract it, pulling the main body of the machine along if the metal tang successfully anchors onto a surface.
These cybernetic crawlers were featured at a Make:Tokyo meeting recently, and managed to lull the audience into a false sense of security with their adorable, snail-like cuteness. Thankfully, they also move as slow as snails. I guess that means they won't be joining the robot insurrection any time soon.