They had become separated. Herobrine hadn't planned for that to happen, but when he noticed something shining across the cavern he decided to check it out. Steve was busy looking down a rather deep hole and didn't notice that Herobrine had left him.
"I would hate to fall in that." muttered Steve, not noticing something coming towards him.
Herobrine looked at the shining ore; it unfortunately had a green color. Herobrine had no need for emeralds, all he wanted were diamonds. He was considering just mining the emeralds to add to his collection of treasures when he heard a yell.
Herobrine ran over to where the yell had originated. He found Steve cowering in a corner with his pickaxe flung across the room. Just over Steve, a bat was flying around curiously.
"Steve…" Herobrine sighed.
Steve looked up and noticed that Herobrine was there.
"Herobrine, is this another one you made?! Is it like the skeleton and green creature? I don't want to die! Make it go away please!"
Herobrine shooed away the bat. "Steve, it's just a bat. It won't hurt you in any way."
Steve stood up. "Oh! I was really worried."
The bat ended up flying into a wall.
Herobrine stared at the bat weirdly. "Notch made these, but I have no idea why he would, they are pretty pointless."
He looked at the bat for a little longer, but then turned away.
"Come on Steve, we need to find diamond."