I haven't tried it yet, but the "Pro Perl" book is a little more explicitly clear:

If we want to use Perl modules that themselves make use of underlying C code (also called extensions), we have to go back and adjust the workings of our interpreter a little. In order to know how to load in the C library part of a Perl extension, the interpreter needs some additional help, which we provide by supplying a function pointer as the second argument to perl_parse. The function performs the job of bootstrapping the external C part of any extensions we want to use. Typically, we use the Dynaloader to dynamically load any modules on demand, so this is the only module we need to handle for most cases.