All of these situations may cause a temporary delay and necessitate extra efforts from the cat, or they may result in complete obstruction.
Behavior that is inhibiting
When the kitten is already through the maternal pelvis and protruding through the vulva, a late manifestation of inhibitory hysterical behavior may cause delay. This may cause some discomfort, so the cat appears to give up and waits for, or demands, assistance at this point. If this is not done right away, the kitten in question may die, especially if it is coming tail first.
The preceding was a rather intimidating, but far from exhaustive, list of what can, but rarely does, go wrong. Breeders and owners may want to know what can be done to detect problems early on and how to avoid or overcome them.