Hibernation

"'This place is safe. Stay here to hibernate.'" Shelters or hibernation pods are self-sealing chambers the slugcat uses for hibernation between cycles. Fully resting one of these rooms is the only way to save the game and one of the ways to progress one's Karma level. Resting within one of these rooms is the only way to survive the rains and proceed to the next cycle.

Normal function
The total amount of food available to spend at shelter is denoted by the food pip circles at the bottom left corner of the screen. Only those circles to the left of the vertical line must be filled to fully rest, and only that quantity will be spent during one hibernation. The food necessary to hibernate varies with difficulty: Entering the square chamber of a shelter with the minimum amount of food will initiate sealing process and begin the new cycle. If the slugcat is lacking minimum food while entering, the unfilled food pips will flash red.
 * Three food pips for The Monk (yellow slugcat)
 * Four food pips for The Survivor (white slugcat)
 * Six food pips for The Hunter (red slugcat)

Starvation mode
The slugcat may force hibernation with any quantity of food by holding down in a shelter. All food will be consumed and the next cycle will take place. Consequences of hibernating without complete food are that the game will not be saved, and the slugcat will enter starvation mode. In this state, the slugcat will have ill-color, and will weigh less than a healthy slugcat.

In starvation mode, the slugcat will intermittently enter a lethargic state where its eyes close and it will attempt to regain composure. During these seconds-long periods, the slugcat moves slower, has weaker jumps and will occasionally cease function for a few moments. During the latter instances, the slugcat will drop any items it is carrying in its hands.

In order to end starvation mode, the slugcat must hibernate with a number of food pips equal to the difficulty's minimum plus those missing from the last cycle. This new food requirement will be reflected by a shifting of the vertical line among the food pips.

Trivia

 * To fill unfilled food pips, the slugcat will consume all food items present in the shelter as it hibernates. Food consumed this way can have the slugcat meet the minimum food requirement.
 * Hibernating in shelters is necessary to the completion of the game's achievements. All achievement progress during the cycle will be saved and displayed during hibernation.