Bob ran down the road.
He fell over.

Bob ran down the road but fell over.

The thunder roared.
The hobbits hid.

The hobbits hid because the thunder roared.

Bilbo slept in a cave.
The goblins attacked.

Bilbo slept in a cave but when he was the goblins attacked.

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

The cart came to a wheezing halt but there was a hobbit hole nearby, so Gandalf strode into it.

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

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

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

Owls are nocturnal so they are active at night, and they have excellent eyesight.