It's been a long time since I read Doc Smith's Lensman series. (Too long!) But when I read this question on English Language and Usage asking for a subtle metaphor for stupidity, Zabriskan Fontema instantly popped into my brain.
What did they do, or not do, that made everyone agree they were the stupidest creatures in the universe? All I remember is that they were circular, and rolled along until they hit something and then turned at right angles and continued to roll along in the new direction. Not bright, obviously, but the stupidest of all? What am I forgetting about their behavior?