I remember looking at the groove in the bread and thinking about some kind of cutaway-like image, something buried. What I like about this is the bone sticking up through the dirt showing the person depicted that something is underneath. We get to see that something.
The ideas come to me as I am having breakfast with one of my sons. This bag probably took me about a minute or 2 to realize the idea, 2 to 3 minutes to draw. Most of the bags take a little less time.