B O O
[ ∞ ] Sweet little Boo never got over Sulley and became obsessed with finding out what happened to him. She remembered that doors are the key to finding Sulley. Later on in life she figured out how to time travel (using wooden doors) and goes back to the source of all magic, "the-will-of-the-wisps" and creates magic to find Sulley by using wood. Boo leaves evidence behind in Brave: two carvings whittled out of wood. They were Sulley and a pizza truck, the two things she loves most in life. Although she knows how to travel through time, she does not know how to determine what time period she will go to. Therefore, speculation has it that Boo is the one planting the easter eggs throughout all the Pixar movies because she has been accidentally going through different time periods.
