“A can of worms”

“By the skin of your teeth”

Barely; just in time.

“Get out of hand”

To become uncontrollable.

“Speak of the devil”

The person you were talking about appears.

“Piece of cake”

Something very easy to do.

“Fish out of water”

Feeling uncomfortable in an unfamiliar situation.

“Out of the blue”

Unexpectedly.

“Take it with a grain of salt”

To not completely believe something.

“Bite off more than you can chew”

To take on too much responsibility.