What are some things that make you go: hmm?

Today for me it is headlamps.

No matter what I do, get a dual package, install them simultaneously, examine the filaments, never touch the bulb, one always goes out before the other. On the other hand ten years of driving and I’ve only replaced one tail light. What is that..

So you get the idea. Something pretty minor that puzzles you seems illogical confusing or baffling. Maybe we can help solve one anothers little mysteries.