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 as the thunder roared.

Bilbo slept in a cave.
The goblins attacked.

Bilbo slept in a cave when the goblins attacked.

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

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

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

Jim rang his friend since he was interested in the idea.

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

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