use strict;
use warnings;

my $foo = "The frog kissed the woman and became a man.";

print "$foo\n";

my %replace = (
               "frog"  => "toad",
               " man"  => " boy",
               "woman" => "girl"
               );

foreach my $find (keys %replace) {

  $foo =~ s/$find/$replace{$find}/;

}

print "$foo\n";