Clever (or not-so-clever) metaphors

Learning a foreign language was once described to me as a snowball--it just keeps getting bigger and bigger, the more you study the language, and if you lose a part of it, the snowball falls apart and there are problems because the snowball is then no longer a snowball. This helps when explaining to students why it's important to keep up on everything you have learned in the foreign language so far, and not let some vocabulary or grammar rules slip, since eventually you'll need those words/rules again and if you've learned them for the test and promptly forgotten them or just plain never learned them, you'll have problems later on. It's better to just learn it all at the right pace and keep up with it. Anyway, I love metaphors and I thought this metaphor was perfect.

Until I moved to the South.

I know it barely snows down here, but it never crossed my mind that IF these kids have seen snow, they've probably never even had enough to make a snowball (although the world shuts down, apparently, at the hint of snow...that'll be interesting). At the beginning of the year, I explained this metaphor to all of my classes, but I think they all just let it go in one ear and out the other. I was re-explaining this metaphor to my accelerated class (they're doing German 1 and 2 in one year, so I was emphasizing the importance of keeping up on everything we've done so far, since this is a faster-paced class), when someone interrupted me and said, "But Frau, we've never made a snowball. We don't know what that's like." I stopped dead in my tracks (probably mid-snowball mime) and really thought about that. Whoa. Poor babies. They've never had the joy of making a snowman...so many childhood memories not made!!

So I've been trying to think of another metaphor but haven't found one. I briefly considered explaining it like a recipe that needs all it's ingredients for the entire time you're baking, but my students are way too literal with everything I say and would probably find weird loopholes (like the one time their Grandma accidentally left out the butter but made the best cookies ever, or something unlikely like that) or they would retort that no one bakes anything for such a long amount of time.

I guess I'll just stick with the snowball metaphor for now and reminisce on my snowman days for my poor snowless students ;-)