sub display_thing (_) {
    print $_[0]
};

$_='Hello 5.10';
display_thing;

##</code><code>##

my $old_display_thing = \&display_thing;
*display_thing = sub {
    if (@_) {
        &$old_display_thing(@_)
    } else {
        &$old_display_thing($_)
    };
};

##</code><code>##

sub display_thing {
    for (@_) {
        print "Displaying thing >$_<\n";
    };
};