Play with other peoples' lexical variables
PadWalker is a module which allows you to inspect (and even change!)
lexical variables in any subroutine which called you. It will only show
those variables which are in scope at the point of the call.
PadWalker is particularly useful for debugging. It's even used by Perl's
built-in debugger. (It can also be used for evil, of course.)
I wouldn't recommend using PadWalker directly in production code, but it's
your call. Some of the modules that use PadWalker internally are certainly
safe for and useful in production.