Your array only has a single element. I'll show how you would split each big string into smaller strings of 2 letters each using a regular expression. Each 2-letter word is stored in a hash.

use warnings;
use strict;

my $length = 2;
my $str = "BEBEBEHUHUHUJJFAFALL";

my %cnt;
while ($str =~ /(.{$length})/g) {
    $cnt{$1}++;
}

print "Found:\n";
print "$_ $cnt{$_}\n" for sort keys %cnt;

__END__

Found:
BE 3
FA 2
HU 3
JJ 1
LL 1
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