From perlmod:

Five specially named code blocks are executed at the beginning and at the end of a running Perl program. These are the BEGIN , UNITCHECK , CHECK , INIT , and END blocks.

These code blocks can be prefixed with sub to give the appearance of a subroutine (although this is not considered good style). One should note that these code blocks don't really exist as named subroutines (despite their appearance).

So - you cannot access BEGIN.