Fetus

The Fetus is undoubtedly the most confusing entity. Not much information is given and only a handful of facts are known about the baby.

Dialogue
The fetus only has one paragraph of dialogue in the Teaser. This can be found in the Halls of Insanity upon entering the bathroom:

''You got fired, so you drowned your sorrows in booze. She had to get a part-time job working a grocery store cash register. Only reason she could earn a wage at all is the manager liked how she looked in a skirt. You remember, right? Exactly ten months back.''

The Final Puzzle
We know now he is required to laugh to get the phone to ring. There are many theories on how to make him laugh, but few methods are proven to work. In total, he needs to laugh three times.

All methods are unlocked after midnight. These can be done as soon as the clock changes. You do not have to wait for the chimes to end.

Walk exactly ten steps, then wait. It takes roughly two seconds for him to recognize it.

Say the name of the letter J into a microphone connected to the system. Other words and names beginning with J (such as Jareth) seem to work as well.

Stop moving and the controller will shake. Wait until after it stops shaking and the phone will ring.

Facts

 * The laughs can be triggered during the ghost's hauntings.
 * The laughs can be triggered at any location.
 * The J laugh can be triggered earlier by saying it before midnight and having the game register it after the chimes.
 * The J laugh can be triggered on the Pause menu.
 * The ten-step laugh can be triggered backwards.
 * You can still complete the final puzzle if the ghost possesses you (although it will be slightly more difficult as she can then kill you).
 * You do not have to look at anything to trigger the laughs.

Myths

 * There is no confirmed way to complete the final puzzle without a voice-activated peripheral. Claims of this working have been made by streamers with microphone enabled cameras or did not realize they had one plugged in.