Both are eating, both old and new moon are receiving light from the sun. Old moon is looking backwards with mouth as the upper half of an hour-glass. New moon is being born from an elbow, with a nutty head and lower jaw like the spur of a cock (as in hoea).

And then we have the double glyphs at the start of each period, here exemplified by the 3rd period (with both wing and eating hand): 

The first of them looks newborn, the last one is old enough to soon give birth and somewhat similar in form to the last glyph in 4a2.