Secret skill

There are several secret skills in The Sims 2.

Meditation
Meditation is a skill that from teens on up can learn. While a Sim meditates, their vitals; like Energy or Hunger; decay at a much slower pace than if they were not meditating. If you have your sims meditate for a certain amount of time, they could learn to teleport.

Parenting
This skill, unique to the FreeTime expansion, can be learned by reading a book from any bookcase. Once learned, it allows a sim to 'check' on babies.