Taking a shit

"a shit" here refers to the act of defecating, not to the feces itself. It's the same as "taking a break" or "taking a vacation" or "taking a look."

It's being used as an action, not a noun. Similar to "taking a break" or "taking a trip". ETA: the "take a [action]" comes up a lot in English. Take a look. Take a guess. Take a nap. Take a walk. Take a bite.

Good question. If you said you were leaving a shit. To me that means that you intend to not flush it. But we also say "I'm going to take a nap" I think "take" might just be getting it's meaning stretched. 

It's what comes out of your rectum, so we colloquially call it pooping.

Maybe you should start a Little Free Library.

‘Take’ has many uses. The one that’s relevant here is “*make, undertake, or perform (an action or task). ‘Lucy took a deep breath*’". Note that “take a shit” is an American usage; British usage would be do/did. Not sure about elsewhere.

I don't think there's a consensus on the evolution of the idiom but I think it comes as a contraction of "taking time for a shit", like to take being a generic way to say to incorporate an action into your day.

Take refers to the activity, not the object being expelled. It is in the similar vein as taking a shower, taking a break, taking a walk, taking a vacation. In this sense "taking" means "performing [an activity]."

Now "taking the piss" is a whole other thing.

[I'll let George Carlin answer this one](https://www.youtube.com/watch?v=fxyw38tODKg)

Need shit? Take a shit. Have shit? Give a shit. j/k

It’s more like “taking a restroom break to shit” = “taking a shit”

Taking = Doing it / Not done Leaving a shit would be implying you are done which wouldn’t make sense if you are still doing it