As implied by above comments, "Threads" relates to Perl 5.0 threads, whereas "threads" (note case change) is the new model introduced in 5.6 and avail for user from 5.8.
See Description section here http://perldoc.perl.org/perlthrtut.html
Basically, the various tutorials/hints I used all said to avoid "Threads".

Cheers
Chris