Bob ran down the road.
He fell over.

Bob fell over because he ran down the road.

The thunder roared.
The hobbits hid.

The hobbits hid as the thunder roared.

Bilbo slept in a cave.
The goblins attacked.

The goblins attacked and the bilbo slept in a cave.

The cart came to a wheezing halt.
Gandalf strode into the hobbit hole.

The cart came to a wheezing halt and Gandalf strode into the hobbit hole.

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

Jim was interested in the idea, so he rang his friend.

Owls are nocturnal.
This means they are active at night.
They have excellent eyesight.

Owls have excellent eyesight and are nocturnal which means they are active at night.