What you're trying to get to is the reference to your piece of data. It doesn't matter how deep it is. At that point, you want to dereference it.

What you were doing was to dereference the array, leaving you with an array. Then ... you tried to take an array and dereference it into an array. That doesn't work as you were expecting (as I'm sure you noticed). :-)

print( "$_ ", join( ', ' => @{$hoa{$_}[0]} ), "\n" )
    for sort keys %hoa;
[download]

You don't need the -> if it's a HoLoL, or whatever. But, you can leave it in if it improves readability for you.

for my $key (sort keys %hoa) {
    print( "$key:$_ ", join( ', ' => @{$hoa{$key}[$_]} ), "\n" )
        for @{$hoa{$key}};
}
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That'll get you all the way you want to go.

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We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.