Here are some common animal idioms in English.

To be a chicken / to be chicken livered

To be a chicken is to be a coward

• I can’t believe that he asked her out yesterday. He is such a chicken.

To be like a dog with two tails

When you are like a dog with two tails, you are very happy.

• When he found out that he’d won the first prize, he was like a dog with two tails.

Gone to the dogs

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

• The business has gone to the dogs since he became the CEO.

Like a fish out of water

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

• When she started talking about her ex-boyfriends, he looked like a fish out of water.

Something is fishy

When something is fishy, it is suspicious.

• There was something fishy in the way he answered my questions.

To be a fly on the wall

To be a fly on the wall is to want to be somewhere secretly, so that you can overhear what is said

• 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.

• He managed to escape before the police arrived. He is a sly old fox.

To get someone’s goat

When something gets your goat, it really upsets you.

• The whole time I was singing she kept herself busy talking on her phone. She really got my goat.