Great subtle enhancements. In your second image you’ve played with the following ideas:
Your first image of the un-eaten cookie is flat, boring and lacks texture. The overhead lighting sucks the life out of the image. Your second image however, you’ve changed your angle slightly and used a shallow depth of field and chocolate chips to help give the photograph some depth. The chocolate chips give the image actual depth with your aperture setting gives the impression of depth.
Secondly, the first image of the un-eaten cookie doesn’t tell a story. However, the bite in the second image adds to the photograph because it tells a story. A basic story, but a story nonetheless. Visual communication is an important part of photography. It’s not always just about pretty images, it’s about saying something without words. I like to see how you’re starting to experiment with this idea.
Thirdly, your image with the bite of the cookie has various textures in both the crumbled cookie from the bite and the chocolate chips. By adding the element of texture to your photograph you’re helping enhance the artistic impact of the image.
I also like how the lighting is less flat in your enhanced image. The lighting trails off in the background which helps to isolate your foreground and enhance to feeling of depth.