You must look for stems in all directions. Forget about stems. Let's start with color. Most apples are red, but then again some are green. I guess a bad apple might even be brown.
Apples are other things too.
For example, most apples are a little bit shiny. They reflect light well, but not as well as a mirror. A mirror is something that shows an image of you and what's behind you when you look into it. I don't know what I look like, or what's behind me - I only have one camera. Ok, forget about the mirror.