use strict;
use warnings;

my %seen;
while (<DATA>) {
	!$seen{ $. . $1 }++ and print "Line $.: $1\n"
	  while /(\b\w{3}\b)(?=.*\1)/g;
}

__DATA__
foofoo
foo foo
foo bar foo
foo bar foo bar
foooof
foo oof
foo and bar
foo foo and and bar bar
foo and bar foo and bar
and or and or say or say or say or say