Great, well you know that @_ would hold the arguments passed to a subroutine and you correlated that with array element indexing. Function (subroutines) parameters are passed either directly or by reference, but you have to remember:

• using & to call a subroutine would disable prototype checking on the arguments if you have specified a subroutine that accepts certain types of arguments.
• modifying a reference inside a subroutine would modify the original data as is the case with references modification in general.