What comes out of the rock crack?

Goblins came out of the rock crack.

"At that he woke up with a horrible start, and found that part of his dream was true. A crack had opened at the back of the cave, and was already a wide passage. He was just in time to see the last of the ponies' tails disappearing into it. Of course he gave a very loud yell, as loud a yell as a hobbit can give, which is surprising for their size. Out jumped the goblins, big goblins, great ugly-looking goblins, lots of goblins, before you could say rocks and blocks."