But that still puts an arbitrary (low) limit on the number of repetitions. The code below doesn't:

#!/usr/bin/perl

use strict;
use warnings;

$_ = 'cat';

s/(.)/my $t = $1; $t .= $1 while 0.95 > rand; $t/ge;

print "$_\n";

__END__
cccccccccccccaaaaat
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Abigail