Have you tried below -1? or non-integer inputs?
Below -1 reports the same thing as the block shown and non-integers round to the closest integer.
Oh. So nothing with complex numbers with Bignums on?
Look, here's basically what it does with the number of variadic inputs.
Complex numbers would also just be too big and I'm pretty sure would crash snap, so there's not really any reason to test it. I don't know why you keep trying to find some weird hidden thing, when it clearly can only display a non-negative whole number of slots (there would have to be code to display a negative or fractions number of slots).
Too big? I said with Bignums ON!
Bignums being on does not change how numbers behave, so it still wouldn't allow negative or fraction inputs.
No, complex numbers with Bignums on! 
Ok.