Hash keys have to be unique, but you can use something like this:

#!/usr/bin/perl

use strict;
use warnings;

my %hash=(
    rat=> [ "acggghhh", "fhhfjfjj", "dggdgdgdg" ],
    mat=> [ "dhhdhdhdh" ]
);

foreach my $key (keys %hash) {
    print $key, "=", @{ $hash{$key} }, "\n";
}
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