Fakeness of The Stone

A few things were off in this film, but the thing that really was noticeable for me was the fakeness of the stone.
Okay, they aren't going to give the actors a 400 pound stone to lift, but at least make it fifty or sixty pounds to make it have some body.
Countless times you can see the stone is almost weightless and moves when barely touched or the actors are trying to make it look like it is heavy when it is obvious it jiggles around like a piece of styrofoam.
This happens quite often in movies and I don't understand why directors don't notice or think audiences don't.