Nature does not neatly divide life into predator and prey or carnivore and herbivore.
To illustrate this, I have this extraordinary photo. I took it in 1997 in Dublin, Ireland. It is a picture of a slug eating a worm. I have no idea how it caught it, and the worm was wriggling madly but to no avail. I doubt that people will believe this picture but its true anyway.
On some northern Scottish isles, sheep eat seabird eggs and chicks (probably for the calcium and nutrients in a deficient environment). This I have read but not seen.
Blurred borders are common in nature. Why? The borders are conceptual and we invented them.
Often no such border exists and faithfully believing in them cuts us off from a reality which is not as clear cut as we imagine!
Life is all the more interesting because of this.
Here is another slug picture. It is the first banana slug that I have ever seen and it is eating a banana! When i pointed it out to my wife and said "its a banana slug!" (as a joke), I was very suprised at her response. "It IS a banana slug!" We were walking to a park to see salmon spawning at the time.