When you call a function without braces i.e. &func instead of &func(), a shortcut happens.

In the words of 'man perlsub':

If a subroutine is called using the "&" form, the argument list is optional, and if omitted, no @_ array is set up for the subroutine: the @_ array at the time of the call is visible to subroutine instead. This is an efficiency mechanism that new users may wish to avoid.