Just did a partial-assist on my third egg - it internally pipped well over 24 hours ago and long before the two that have hatched, but no external pip and the cheeping was getting weaker. I carefully opened up at the air sack, found where the chick had pipped, but no sign of a beak. Peeled back the membrane a bit to discover that the dummy had pipped, then decided to flip around in the egg! It's still not ready to come out, but it's back to peeping bloody murder at me, so that's a comfort!