#!/bin/perl -w
use strict;

my %sentence_count;

foreach my $sentence(<DATA>) 
  { $sentence=~ s/^\W+//;                 # remove leading non-words
    my $counter = split(/\W+/,$sentence); # split on non-words sequence (\W+)
                                          # in scalar context split will return 
                                          # the number of elements in the generated list,
                                          # no need to count them ($count= @word in your 
                                          # example would work too)
    $sentence_count{($counter)}++;
   }
   while ( my($sentence_count,$word_count) = each(%sentence_count)) {
           print ("There are $word_count sentences of $sentence_count words\n"); 
           }
__DATA__
one
one
two, two
two. two
two, two.
three three three
 three three three
three three three.
three three, three