I have a bone to pick with you.

Picking bones? Yuck!

I have a bean to pick with you.

You're beating a dead horse.

This implies that it's useful to beat a living animal.

You're wasting your time or You're beating a worn rug.

Kill two birds with one stone.

Why would anyone want to kill one bird, much less two?

Feed two birds with one seed.

Blind as a bat.

Although they rely strongly on echo-location ("radar"), bats have very good vision.

Blind as a turnip or Totally blind.

This place looks like a pig sty.

If left to themselves, pigs keep their homes very clean. It's only when they're in captivity that they are forced to live in their own filth.

This place looks like a garbage dump or This place looks like a teenager's bedroom ;-).

Raining cats and dogs.

An expression dating from the Middle Ages. Homeless and neglected cats and dogs died in great numbers, and their remains were washed along the city streets when it rained heavily.

Raining waterfalls or Raining torrents.

That's a whole other kettle of fish.

Fish belong in their native oceans, lakes, rivers, and streams, not in a pot.

That's a whole other sack of beans or That's a whole other cup of tea.

What's sauce for the goose is sauce for the gander.

You mean ex-goose and ex-gander.

What's sauce for the pasta is sauce for the rice or What's good for the goose is good for the gander.

Make a monkey out of someone.

It implies that monkeys are foolish, and that their behaviour is embarrassing.

Make a fool out of someone.

S/he's a dog.

It implies that both the person and the animals are ugly.

Nothing. This is simply a crude and cruel remark, insulting to both people and animals.

S/he's being catty.

Cats are not mean, and never make unkind remarks about other cats (or people!).

S/he's being mean.

You can't make a silk purse out of a sow's ear.

To make silk, the silkworms are steamed alive in their cocoons. And the idea of cutting off someone's ear!

You can't make an evening gown out of a dish rag.

Give a man a fish and you'll feed him for a day. Teach a man to fish and you'll feed him for life.

Why do you need to kill animals to eat?

Give a person vegetables and you'll feed him (her) for a day. Teach that person to grow vegetables and you'll feed him (her) for life.

There are plenty of other fish in the sea.

And that's where they belong!

There are plenty of other leaves in the tea.

There's more than one way to skin a cat.

Sami, Pitzi, and Shana hope there's no need to explain this one. =^.^= (A kind reader pointed out that this expression refers to catfish, who are covered with skin rather than scales. Sorry, we've lost the email; if the reader will contact us we'll credit you!)

There's more than one way to bake a cake or There's more than one way to brew green tea.

And here's one that's not about animals, but so many people use it without realizing what its offensive origins are that I decided to include it here anyway.

As a rule of thumb

This refers to an old English law that the thickness of the stick a man could use to beat his wife could be no thicker than his thumb.

As a general rule ... or A good guiding principle is ...