It's B::Xref and it's pretty cool.

There is also a Devel::Xref which I eventually pursuaded CPAN to allow me to download.

However, the documentation is less than clear (to me) on how to use it. I can get some output, but you have to embed it in the script, and the output is somewhat confusing.

Now you've pointed out B::Xref, and demonstrated how easy it is to use, I am way impressed. It is really cool. And fast!

I just tried it out on Date::Manip. Very interesting, if slightly scary reading.

Thanks for posting, I can see me using that a lot.