[C++] Pointer to function giving error

[System_Error]

I have a very simple function pointer that I even got out of a book, but my compiler (dev cpp) is giving me the following errors:

35 C:\Dev-Cpp\main.cpp invalid use of non-static member function `virtual void Mammal::speak()'

35 C:\Dev-Cpp\main.cpp cannot convert `void (Mammal:()' to `void (Mammal::*)()' in assignment


The code is as follows:

#include <iostream>
using namespace std;

class Mammal
{
  public:
         Mammal() { }
         virtual ~Mammal() { }
         Mammal(const Mammal&) { }
         
         virtual void speak()
         {
            cout << "Mammal speak\n";
         }
};

class Cat: public Mammal
{
      public:
             Cat() { }
             ~Cat() { }
             Cat(const Cat&) { }
             
             void speak()
             {
               cout << "Meow\n";
             }
};


int main(int argc, char* argv[])
{
    Mammal m;
    void (Mammal::*pFunc)() = 0;
    pFunc = Mammal::speak;
    
    Mammal* ptr = new Cat;
    (ptr->*pFunc)();
    
    delete ptr;   
}

What exactly am I doing wrong to recieve this error? Everything looks correct?