Once you've parsed them (which is admittedly much more difficult than Perl), writing a relatively slow interpreter for the core language in C or similar wouldn't be that difficult.
Perl currently has no specification, other than the latest release of the interpreter. What the interpreter does may be decided to be incorrect by consensus at some point, and changed (although Perl has a very strong history of backwards compatibility so it's unlikely to change unless it was unuseful before), but there is no external resource besides the code and the compiled interpreter to explain how it should behave in every case.