Note, there are many ways a BEGIN block can get executed without ever having the word BEGIN in your code. For example:

# In Test.pm
package Test;

sub import { print "Boo!\n"; }

1;

--------------
# In your script

use Test;
[download]

Where's the BEGIN?

There actually was a question/meditation on here about 2 years ago on this very topic. I don't remember the details, but the OP was remarking that he was running into a forking/threading/caching/whatever issue. It turned out that there was a module about 4 levels back into the uses that was doing something he didn't want. And, it was happening at compile-time, so he couldn't disable it.