Its picky, but I personally don't like the use of an iterative approach here (feels like "shoe-horning", kinda like the freaky NT/2000 command shell forces you to use "for" to get simple command substitution) with the "for" and might prefer a form that, nonetheless, still uses $_. I can easily see how folks might dislike that print stmt at the end, though, hmmmm....
$_ = "A man and a woman saw a frog by the pond\n";
s/frog/toad/g, s/man/boy/, s/woman/girl/, print $foo = $_;