In rare circumstances a pair of breeding Domesticated Animals will give birth to a Stillborn instead of a baby. A Stillborn is a Witnessed Insanity structure; each time you see a Stillborn you will gain a moderate amount of Insanity. To stop this from happening a Stillborn must be Destroyed.
Witnessed Insanity is Insanity which is gained by doing insane actions. When witness insane things you will gain Insanity each time you come into range of that thing. This means the same event can cause you to gain a lot of Insanity if you continue to leave and come back to the same area without dealing with the thing causing you to gain Insanity.