An Undergrowth Movement

I think, pretty sure, that they are trying to imply underground. As in secret or subversive.

"Not secret enough", you might say. Before adding, "Anyway, what could possibly be subversive about berry fucking cider?". You'd have a point.

But they actually say undergrowth. As in, well, under growth. Like where berries grow.

I don't know. I suppose it'll just have to be yet another to file under Shit Advertising, Shit Product [1]. If we can be squeeze it in.

[1] of course I haven't tasted it!