There's a puzzle in a Russian kids book for 5th graders, and you have to find the defining characteristic for each group of objects. The first one had metal, the other had ovals, the third had furniture... but we just can't get the last one.
A whale, a penguin, a boot, a piano, and a train.
It's bugging us. We think that we're thinking too complicated, and not simple enough, like a 5th grader would.
Why we're doing 5th grade Russian puzzles is beyond me.