The Yolk Event is a full-screen event added in version 0.03.
During this event, Usotsuki floats sleepily within an empty white space while soft music plays. The event can be exited early with the space bar and can be repeated as many times as desired, but if the player allows the event to finish, Usotsuki will wake up.
How to Reach It
In the Red Sea, there is a blocked-off island of trees that lead to the Painted Hall. The island can be reached via a "bridge" of blinking red dots; if the dots are not there, the player must wake up and try again.
Usotsuki must walk along the "snake" part of the Painted Hall to reach a blocked-off region of Egg World. Along a walkway is an Egg hut with a hole in the ground. Walking into the hole will trigger the event.
Usotsuki will float in the vacuum for a little while; images of a hand and legs (presumably belonging to Usotsuki) will flash, and if the space bar is pressed she will emerge from the hole covered in what seems to be egg yolk. Re-entering the hole or turning on an effect will make the yolk disappear. If the space bar is left alone, Usotsuki will gradually drift downward as the screen lightens and she will wake up.
Due to the fact that the event is accessed inside of an egg, and since Usotsuki must enter the pelvic region of the Painted Hall to reach the event, some players have likened the Yolk event to be a kind of "birth scene."
Usotsuki appears to be falling deeper into the white space before she wakes up; this may be a reference to the reaction that causes people to wake up when they are falling in a dream.