Hidden features of Perl?

I'm depressed to say that I knew most of these. Can I have those braincells back?

Most of them (if not all) are just unpopular features.

<a href="http://stackoverflow.com/questions/161872/hidden-features-of-perl/2911882#2911882" rel="nofollow">http://stackoverflow.com/questions/161872/hidden-features-of...</a>

It can, sometimes and with great skill, be used to write understandable code.