Things You Didn't Know!

There's a whole thread on The Sims Forums with 386 pages and counting.  I will bring out some things from there though.

• After successful attempt at introduction, if your sim proceeds to be rude to the celebrity, they may eventually shun your sim, disabling all the interactions with them.
• From an errand from the Creature Keeper, your sim can obtain food called Mushroom Mash, which allows them to understand birds (you'll get what birds are talking about as a text notification).
• The stereo that comes as a reward from a High School Prom event can play you Prom Night music.
• You can turn Servos into human sims by gifting them a Death Flower scented arrangement.
• Toddlers can destroy unfinished school projects.
• Sims with certain traits like certain toppings on their ice cream.
• There's a hidden colossal head in the oceans of Tartosa, waiting to scare you.
• Brave horses can comfort spooked horses, calming them down.
• In High School career day, three sims called to present aren't from random careers. Sim 1 is either a Space Ranger (Astronaut career) level 10, Chef (Culinary career) level 7, or Doctor level 7, Sim 2 is either a Boss (Criminal career) level 7, Manager (Business career) level 7, or Detective level 7, and Sim 3 is either a Diamond Agent (Secret Agent career) level 10, Professional Athlete (Athlete career) level 7, or Officer (Military career) level 7.
• Babies conceived from the lighthouse woohoo get a special happy moodlet when visiting the lighthouse.

And more that don't come to my mind at the moment...