sub hash_slice {
    my ($hr, @k) = @_;
    return map { $_ => $hr->{$_} } @k;
}

# or using a slice (might be more efficient, but doesn't read as nicely)
sub hash_slice {
    my ($hr, @k) = @_;
    my %ret;
    @ret{@k} = @$hr{@k};
    return %ret;
}

# use like this:
%pets = hash_slice( \%hash, qw( dog cat ) );