Bob ran down the road.
He fell over.

Bob fell over because he was running down the road.

The thunder roared.
The hobbits hid.

The thunder roared so the hobbits hid.

Bilbo slept in a cave.
The goblins attacked.

Bilbo slept in the cave as the goblins attacked.

The cart came to a wheezing halt.

Gandalf strode into the hobbit hole.

Gandalf came to a wheezing halt as he strode into a hobbit hole.

Jim was interested in the idea.
He rang his friend.

Jim rang his friend because he had an interesting idea.