Leap frog
Barn cat
Stray cat
Town mouse
Country mouse
Snowbird
White whale
Working dog
White Lion

Chicken Hearted
Turkey Neck
Silly Goose
Work Horse
Night Owl
Lion's Den
Wolf Pack
Shark Tank
Sitting Duck
Cash Cow
Prize Hog
Golden Calf
Show Horse
Government Mule
Fat Cat
Top Dog

Clothes Horse ~ Laughing Hyena ~ Playing Opossum ~ Scaredy Cat ~ Church Mouse ~ Dirty Rat ~ Hungry Hippo ~ Stubborn Mule  ~ Busy Bee ~ Leaping Lizards ~ Fighting Cocks ~ Guide Dog

Mad dog.
Gift horse.
Wise owl.
Busy Bee.
Beached whale.

early bird
eager beaver
funky chicken
whirly-bird
songbird
stool pigeon 
lounge lizard
mall rat
paper tiger
loan shark
holy mackerel
holy cow
lab rat
charley horse
code monkey 
grease monkey 
hell cat
cry wolf
tom-cat
rug rat
sly dog
chowhound
rockhound
shuttlecock
shutterbug
jitterbug
bookworm
pink elephants
Moscow mule
pink squirrel
brass monkey
black cow
salty dog
cold duck This post was edited by Flint Ironstag at February 28, 2022 3:18 AM MST

Spelling bee
Snow bunny

Loan shark.

Tomato spider - sometimes used within our family when we were young, for the fruit's calix.

Ear-worm

Golden Lion - a quite common, old pub name, in England. Along with various White Harts, Black Dogs, etc.

Nodding donkey - a nick-name for the beam-pump often used on oil-wells holding little or no natural gas-pressure.

Vaulting-horse

Clothes-horse (airing frame)

Saw-horse

Catch a crab - all right, that's three words, sorry! A rowing term.

Fire dogs - log supports used long ago, in large, open fireplaces.

"Soup Dragon" (The) - how well do you know children's TV shows?

Lounge lizard

Spinning jenny - Early textile-trade machine citing now-archaic synonym for "donkey" or "mule". Also, "tinman's jenny", a workshop tool.

Snowman - yes, we 'oomans are animals, biologically!

"Iron Man" - it's a sports event.

"Black dog" - Sir Winston Churchill's nick-name for the effects he suffered, of clinical depression.

Dark horse - of a person surprising everyone in some way.

"Iron horse" - 19C USA colloq. for "railway locomotive". I am not sure if it was also used in Britain, where the machine itself was invented.

High horse - though perhaps inadmissible here as it is normally prefixed with "on his/her..."

White horses - on rough sea.

Spring chicken - of a person. A compliment, except when following "He's /she's no..."

Old Bat - of a person, especially a woman, and definitely not complimentary!

Greedy pig - insult or reprimand!

Cheshire cat - met by Lewis Carroll's Alice. (Cheshire itself is an English county.)

"Dudley Bug [The]". This is an unusual one. The residents of that English Midlands town are proud of their species of trilobite (fossil) common in certain of the rocks of that area, and coined the name as their affectionate appellation for it A trilobite was not actually a "bug" but a marine animal slightly resembling a large wood-louse, typically around a foot long.

Mud lark - coined in 19C London for children of poor families, scavenging for bits of metal in the Thames at low tide, to sell as scrap for a few pennies.

Sex kitten - of a woman: 1960s slang probably now Frowned Upon!

Pompous ass - uses the English meaning of "ass", a "donkey" or mule", of someone pompous but no brighter than the animal. Largely fallen out of use. (The body part is "arse" in British English.)

"Free Bird" - the song.

Guinea-pig - two for the price (£1 1s 0d??) of one as both the rodent and the human volunteer in a medical experiment!

"Mechanical horse" - another equine metaphor, but nearer than some by citing using the animal for transport. This was the popular nick-name at least, for a small articulated-lorry made by the British firm Scammell in the 1940s-50s, for short-journey, urban goods deliveries / collections; typically between businesses and their local railway-stations. The tractor unit was unique in being a three-wheeler, with single front wheel.