“Let the cat out of the bag”

“By the skin of your teeth”

Barely; just in time.

“Curiosity killed the cat”

Being too curious can cause trouble.

“Get out of hand”

To become uncontrollable.

“Speak of the devil”

The person you were talking about appears.

“Fish out of water”

Feeling uncomfortable in an unfamiliar situation.

“The tip of the iceberg”

A small visible part of a much bigger problem or situation.

“Out of the blue”

Unexpectedly.

“Give someone the benefit of the doubt”

To believe someone may be telling the truth even if you are not sure.