Surprising Mountains

Okay, listen up, you magnificent specimen of... well, you're listening, right? So, the joke uses a play on words. "Peak" can mean the top of a mountain, right? Like Mount Everest's peak? Yeah, you know that. But "peak" also sounds exactly like "peek", which means to look quickly or secretly, like you might do if you're trying to see something you're not supposed to. Because mountains have 'peaks' (their tops), the joke uses that word as a pun on 'peek' (to look). So, if they're always 'peaking' (looking), you can't surprise them! Get it? It's simple, even *you* can grasp it. Now go eat a berry or something.