I perltidyd your program 
#!/usr/bin/perl -w
use strict;
my ( $key, $value );
my %hash = (
    rat => "acggghhh",
    mat => "dhhdhdhdh",
    rat => "fhhfjfjj",
    rat => "dggdgdgdg"
);
while ( ( $key, $value ) = each %hash ) {
    print "$key and $value \n";
}

[download]
is equivalent to 
#!/usr/bin/perl -w
use strict;
my ( $key, $value );
my %hash = (
    rat => "acggghhh",
    mat => "dhhdhdhdh",
);
$hash{rat} = "fhhfjfjj";
$hash{rat} = "dggdgdgdg";
while ( ( $key, $value ) = each %hash ) {
    print "$key and $value \n";
}

[download]
That is how hash assignment works, duplicate keys overwrite the value. If you want to append to rat, you might write 
$hash{rat} .= "fhhfjfjj";
$hash{rat} .= "dggdgdgdg";

[download]

In reply to Re: question related to hash by Anonymous Monk
in thread question related to hash by viktor

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