Ubuntu :: Switch Back To /usr/bin/perl After Installing Second Perl?

I recently reinstalled the B module for perl. Now I found out it didn't just do that, it installed a whole new copy of perl into /usr/local/bin/perl. When I type 'which perl' at the terminal, it says '/usr/local/bin/perl' instead of '/usr/bin/perl'. Normally, this wouldn't bother me. But I installed the one in local/bin without threading support. The one that comes with the system already is build with threading support, which is why I want to switch back to the system perl, and possibly remove the one in /usr/local/bin.

So how do I change it so that the result of 'which perl' returns as '/usr/bin/perl'? And what do I have to do to remove /usr/local/bin/perl?

The reason I need threading support is because I'm designing a file copier that copies several chunks of a file simultaneously to speed up the copying process. Guaranteed a useful script if it works.