use strict;
use warnings;

my (%c, @w);
$_ = lc join '', <DATA>;

while (m/([a-z]+(?:'[a-z]+)?)/g) {
    push @w, $1 if !$c{$1}++;
}
for (@w) {
    print "$_ : $c{$_}\n" if $c{$_} > 1;
}