Well, ummmmm....  Consider body functions YOU experience.  If yer a gal in or past the age of child-bearing, you may remember the sensations when you had no control over the onset of menstruation.  Human women "shed" eggs monthly, hens do it daily.  The first few menses can be distressing, with unfamiliar cramping.  Multiply that 30 times.
Over a period of time, hens get used to what their bodies are telling them, able to gauge where in the process they are at a given time.  But those first few eggs...  "Dang!  It's happening AGAIN! What's up with that?!?!?"