Python String slicing results unpredictable or same at different slice indices

Question

I have a string "Queen" and I have the following code snippet:

    string = "Queen"
    print(string[::-1])

Surprisingly it gives the result "neeuQ". But when I do print(string[-1::0]) it says

    ValueError                                Traceback (most recent call last)
    <ipython-input-26-3b86270ea57d> in <module>
          1 string = "Queen"
    ----> 2 print(string[-1::0])
    
    ValueError: slice step cannot be zero

Again when I write print(string[-1::9]) or any other number>0 it shows the same result "n".

I understand this is about Python's string slicing properties but I didn't get the operations that are happening inside for every command. Normally for a string[0::4] it's absolutely fine but what's happening in these cases? Why are we having such outputs?