Why can't I select mirrored faces? So I've mirrored the faces to make a mouth, but can't select any of the mirrored faces, it's as if they are ghost faces.

I've tried selecting faces, going into edit mode and object mode, But I'm new to this app so I don't ave a lot of knowledge about it:
You cannot select mirrored faces. If you want to select them, you need to apply the modifier and from this point you can make the 2 half different.