But why is the sky blue?

Here's a sampling of the random questions I've encountered in the past week that have piqued my interest. I feel like these should be answerable with a little effort (by someone other than me, since my brain is stuck in corners), but they're also fun to just speculate about.

It's a commonplace that Benadryl makes you drowsy. kcr noted that it only seems to make him drowsy when it isn't busy fighting off an actual allergic reaction. Are the antihistamine and sleep-inducing activities of Benadryl different? Does one compete with the other?

Why do martial arts seem to be optimized for fighting other practitioners of that same martial art? I don't know anything about how martial arts develop, but my intuition says something like this: it's dangerous and impractical to always practice by getting in real fights, and if you're going to make a new variant on an existing style, then practicing against others of that style is a decent proxy for being in real fights. Of course, this runs into the bootstrapping problem of where did the first formalized martial art come from... but humans have been punching each other for so many years that I feel like basic instinct can serve as a starting point. (How do you go about designing a martial art for "real combat"? I know these exist -- mumble military mumble something.)

What's the most cost-effective way to make ice cream using a dry ice and ethanol bath?