That has to do with @_ right?

Partially. See this relevant bit from the perldoc:

NAME(LIST);      # & is optional with parentheses.
NAME LIST;       # Parentheses optional if predeclared/imported.
&NAME(LIST);     # Circumvent prototypes.
&NAME;           # Makes current @_ visible to called subroutine.
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So the passing of @_ is affected, as is the prototyping. I'm not too familiar with prototypes in Perl, so I'm not sure how things are affected when prototypes are circumvented... which is why I pointed to the perldocs instead of spelling it out myself. I know there's a difference, but haven't really looked into it. ;)