Idiotic Idioms ?

‘It is raining cats and dogs’ “Is it really” what on earth is that about?
Now that is an idiotic idiom to me without a doubt!!
Try as I may to picture this in my head.. teehee if this was accurate wouldn’t we all be dead?

‘When pigs fly’ Now that would be strange
Porky pink piggies instead of feathered friends for a change..
Zooming through the skies..”Oinking” as they flew 
Oh my goodness they would be pooping on you ?

“Running around like a headless Chicken” hells bells how absurd.. these short sayings are the daftest Iv’e ever heard
Who on earth invented them? I applaud their wacky imaginations
Inventing impossible scenarios whilst they became ‘well-known’ throughout the nations