Hello hurricup,

Which blocks exactly work this way...[?]

There is a non-exhaustive list in perlsub, introduced as follows:

Subroutines whose names are in all upper case are reserved to the Perl core, as are modules whose names are in all lower case. A subroutine in all capitals is a loosely-held convention meaning it will be called indirectly by the run-time system itself, usually due to a triggered event.... The following is a list of some subroutines that currently do special, pre-defined things.

Note also:

The BEGIN, UNITCHECK, CHECK, INIT and END subroutines are not so much subroutines as named special code blocks, of which you can have more than one in a package, and which you can not call explicitly.

By contrast, AUTOLOAD is a (special) subroutine:

13:43 >perl -MO=Deparse -we "AUTOLOAD { 'First' } AUTOLOAD { 'Second' 
+}"
Subroutine AUTOLOAD redefined at -e line 1.
BEGIN { $^W = 1; }
sub AUTOLOAD {
    'Second';
}
-e syntax OK

13:43 >
[download]

Hope that helps,