Funny about the minus sign

I just discovered that there something funny about this minus sign. See if you can guess the output of the following code without running it:

use strict;
use 5.010;
$, = " ";
for my $v (qw(42 FortyTwo)) {
    say -$v, -"$v", -("$v");
    say -(-($v)) , -(-$v), -(-$v);
    say -(-("$v")) , -(-"$v"), -(-$v);
    say -(-(-("$v"))) , -(-(-"$v")) , -(-(-$v));
}

It's pretty easy when the $v is 42, but not quite obvious when it is "FortyTwo". I don't have any explain on it. That's maybe documented somewhere and I'll have to find it.