add hash to hash of hash

[Mark Hanson]

Hi,

Still more hash questions: 

using the example in chapter 9 of Programming Perl:

%HoH = (
    flintstones => {
        husband    =>    "fred",
        pal            =>    "barney",
    },
);

how can dynamically add another hash to %HoH? In Programming Perl, they have a hard 
coded example:

$HoH{mash} = {
    captain => "pierce",
    ...
};

I've tried: 
$HoH{'mash'}{'captain'} = {'pierce'};
and assorted variations...

Pls help! Thanks!
/Mark