Here is a list of animal idioms

To be a chicken / to be chicken livered

To be a chicken is to be a coward.

• Peter is such a chicken. He is afraid of being alone.

To be like a dog with two tails

Used to refer to a person who seems to be quite happy

• When he discovered that he’d won the jackpot, he was like a dog with two tails.

Gone to the dogs

When a business or a country goes to the dogs it becomes less successful or less prosperous than it was.

• If anarchy prevails, the country will go to the dogs.

Like a fish out of water

If you are like a fish out of water, you are uncomfortable.

• She looked like a fish out of water, when she met her ex-boyfriend at the party.

Something is fishy

If something is fishy, it looks suspicious.

• There was something fishy in the way he behaved at the party.

To be a fly on the wall

Used to mean that you would like to be somewhere secretly so that you overhear everything

• I would love to have been a fly on the wall when they discussed their secret plans.

To be as sly as a fox / a sly old fox

When you are as sly as a fox, you are very cunning.

• My boss is a sly old fox. He knows how to get around the tax laws.