Ohh, that brings back (bad) memories.

In $CPAN/src/unsupported/4.036/perl-4.036.tar.gz, you'll find a file named lib/chat2.pl, which contains:

    unless (socket(S, 2, 1, 6)) {
        # XXX hardwired $AF_SOCKET, $SOCK_STREAM, 'tcp'
        # but who the heck would change these anyway? (:-)
[download]

Yes, these were the correct constants on BSD, but they were wrong for SysV, which meant that every SysV user sent me bug reports about why chat2 didn't work for them. {sigh}

Thankfully, that file was "retired" as of Perl5, being replaced by the Expect module.