Think of 'tie' as a way to have an object act like a hash. Perl calls those methods on the object to implement the hash functionality.

my $value = $hash{$key};
my $object = tied %hash;
$value = $object->FETCH($key);
[download]

Most objects are blessed references to hashes; they are implemented as hashes internally. Perl does not have a mechanism for having named attributes (ie instance variables) of an object. People use hashes to store the internal state of the object.

It is quite possible to have a tied hash implemented using a hash reference object.