The Sims 4
The Sims 4
In the Country Life expansion, there is a decoration called "Jerry's Reeds" with the following item description:

"This particular strain of reeds was originally grafted by scientists and doctor's [sic] at St. Mary's Hospital as part of their research into experimental vaccines intended to counter parasitic fungal infections. It never amounted for much, other than it's [sic] ability to attract fireflies."

This item is referencing The Last of Us Part II, specifically the character of Jerry Anderson, the leader of the group of doctors called the Fireflies who were attempting to create a cure for the Cordyceps brain infection at St. Mary's Hospital.
Contributed by MehDeletingLater
If the game detects that you are playing an illegal copy after a Sim finishes any action that uses the mosaic censor, instead of it disappearing as normal the mosaic will not only remain there but will grow until the entire screen is nothing but pixels.
Contributed by ShyanVixen
In The Sims 4, if a Sim is pregnant the player can influence what gender the child will be. If the pregnant Sim eats carrots or listens to alternative music on the radio, the baby is more likely to be a boy. If the pregnant Sim eats strawberries or listens to pop music on the radio, the baby is more likely to be a girl.
Contributed by ByronDoodles
If a Sim interacts with a certain tree, they will eventually be able to explore it. This will unlock a secret area called "Sylvain Glades".
Contributed by generalcodeblue