There is a mountain on top of a bunch of dirt with a steep cliff. This is a bit redundant, but the mountain and the dirt just make the cliff even bigger and steeper and scarier.
As you’re peering over this tall cliff, somebody behind you shouts, “Hey, guy (がい)!” This startles you and you tumble down the cliff. Apparently so did he, because you can hear him saying, "Hey guy! OOF! Are you okay? OOF! Guy? Guy!!!” as you both fall.