It is almost axiomatic among mid-level trained Christians that the reason for God having rejected Cain's sacrifice in Genesis 4 is because it was not an offering of blood. Therefore it seems obvious that God must have cued both Cain and Abel in off-the-record regarding what constitutes a proper sacrifice. Because from my point of view, Cain's offering seemed fair - both brothers offered out of the inventory of their profession. The Genesis account does not tell the reason. I am left to surmise that the differences in acceptance has something to do with the heart in which the offerings were presented.
While I don't want to trivialize phenomenal weight of the sacrificed blood, I read Leviticus 2 and I wonder - is the blood the real difference in the offerings? I suspect that KJV reads "meat offering." In the 1600's, I think meant any food that was not liquid, such as Pepsi. Since the modern day concept of meat is covered in rams, goats and turtle doves (chicken?), the Leviticus 2 classification of meat would then be all solid food that is not meat - fruits, vegetables, bread, french fries, and the like. Some modern versions refer to them as Grain Offerings.
If offerings must include blood sacrifice, then what should we make of the Grain offerings of Leviticus 2?