virtual function declared non-virtual in a derived class

Question

If a function is declared non-virtual in a derived class when the base class function was virutal, why does it invoke a vtable lookup on calling the function on its pointer? The

Answer 1

In C++ if you declare a method virtual in the base class then it's virtual also in derived class, even if the virtual keyword is omitted.

For documentation purposes is however in my opinion nice to repeat it anyway.