Bob ran down the road.

He fell over.

Bob fell over, because he ran down a hill.

The thunder roared.

The hobbits hid.

As soon as the thunder roared, the hobbits hid.

Bilbo slept in a cave.

The goblins attacked.

While Bilbo slept in a cave, the goblins attacked.

The cart came to a wheezing halt.

Gandalf strode into the hobbits hole.

When the cart came to a wheezing stop, 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.

Owl are nocturnal, this means they are active at night and they have excellent eyesight.