The best reason to avoid clichés in writing is that they are boring.
The next best reason is some are just plain wrong and it’s our job as writers to stop the spread of ignorance:
Sweat like a pig.
Pigs don’t sweat, at least, not enough to matter. That’s why they wallow in mud — they need a heatsink.
However, apparently this expression really refers to pig iron anyway, not pigs. So maybe this doesn’t exactly prove my point. Oh well. Moving on…
Blind as a bat.
Bats aren’t blind. They see very well when there is light, but of course, their thing is seeing in the dark. For that, they developed sonar. But their eyes didn’t suddenly stop working when they started squeaking at mosquitoes.
There are truly blind animals. Why not use “blind as a Texas cave salamander”? Or even “myopic as a mole”. Hey! that one is pretty good. You can use it. Until it becomes cliché.
Drink like a fish.
This is either completely wrong or mostly wrong, depending on whether you are talking about fresh or salt water fish:
– Freshwater fish don’t drink at all. They absorb all the moisture they need from the water passing through their gills. So you can’t “drink like a fish” unless you have gills or the ability to absorb water through your skin. Tadpoles and frogs can do that. So why not “drink like a frog”?
– Saltwater fish do swallow a little water to replace what they lose from their gills due to osmosis. Occasional little sips. I don’t think that is in the spirit of the expression.
Slippery as a snake.
Snakes are not slippery, they are smooth. If something is slippery, you can’t get a proper grip on it, like a wet bar of soap, or a politician’s promise. Snakes are dry (except, obviously, for water snakes) and you can hold a snake easily. If you want to test this yourself, remember if it wasn’t for snakes we would be buried in vermin, so don’t squeeze hard enough to hurt the little fella.
Slippery as an eel works, but you lose that attractive alliteration.
Piss like a racehorse.
Does that mean naked, on all fours, in the middle of a racetrack? While possible, it is a physically challenging pose for women and probably not a good idea for men either.
I smell a rat.
Rats don’t have a scent that humans can detect. You may smell a rat’s nest, but again, probably not — our noses are terrible.
On the other hand, humans have a scent that just about every animal can detect. We are a truly rank species. Even a few days without bathing will do it. So you should say “I smell a human”.
Working like a dog.
Okay seriously — when was the last time you saw a dog working? My dog naps, begs for treats, and chases things. So does every dog I know. Even so called working dogs, like retrievers and sheepdogs, don’t look they are working. They look like they are having a blast.
If only our jobs made us so happy.
If my job was sniffing butts and wallowing in bellyscratches, I’d work like a dog too.
* Isn’t “as retired as a raphus cucullatus” more interesting than “as dead as a dodo”?