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? (:-)
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.
