Feeding behavior

After adding shrimp and krill to my RPB's diet, I have noticed that he circles the food lying on the bottom and then flips sideways and rubs himself on the gravel and food. He only does this with non-live food. He does not do it after the food is gone and he does not do this if the food was live (such as half a feeder laying on the bottom). Has anyone else seen this behavior from their p's? Is this just something they do? Thanks for any info anyone can give.