STRINGS.CODEX.CRITTERSTATUS.MOOD.HAPPY.CONTAINER1
Happy, tame critters produce more usable materials and tend to lay eggs at a higher rate than glum or wild critters. Domesticated critters are less resilient than wild ones—they require more care from the colony in order to maintain a positive disposition.
Babies have a higher baseline of natural joy, but produce neither resources nor eggs.
Duplicants with the Critter Ranching skill have the expertise needed to domesticate and care for critters. They can boost a critter's mood and tend to their health at a Grooming Station.
Critters who drink at the Critter Fountain also enjoy a mood boost, despite the lack of nutrients available in the Brackene dispensed.
Being confined or feeling crowded undermines a critter's happiness.