Brain to body ratio.
While not at the bottom of this category, the ostrich is close. Its 1.5 ounce brain steers a 250 pound bird.
What animal is at the bottom of this list? No one is sure, but answers swerve between the Bony-eared Assfish and the American politician. (I threw this detail in because I simply wanted to type the word assfish a second time).
As Job 39:17 reminds us "God did not endow her with wisdom or give her a share of good sense" (the ostrich, that is).
Here's a big male from the Tanzanian grasslands.
Safari with us and see a silly ostrich for yourself.