my %react_to = (
    walk => sub { print "Walking is good for you\n" },
    park => sub { print "Parks are fun\n" },
);

my $text = "I am going to walk to the park.";

for ($text =~ /(\w+)/g) {
    if (my $reaction = $react_to{lc $_}) {
        $reaction->();
    }
}