I’m presenting these in the order that I found them, not because it makes more sense that way, but because it makes slightly less, and then you can share in the somewhat befuddled but interested discovery process.
I came across this video on Boing Boing:
And it’s sufficiently addictive (catchy song, amusingly random, cute girl, probably all of the above) that I watched it a couple of times. I eventually decided (a couple of days later with it still stuck in my head) that I was going to figure out where it came from.
So, I eventually figured out that there’s a game called Plants vs Zombies that you can play the first few levels of online for free. It’s an okay game, a decent time waster, but nothing too spectacular. But once you play it for a while, the song starts making more and more sense (still not lots, but more at least).
So, even more eventually (at least a week, maybe two, since watching the first video, as I played the game on and off 5 minutes at a time in the evenings until I ran out of free levels) I watched the video on youtube, and in the related video section was this, which sort of made it all come together: