Your sister
[Scene: Luke, age 7, has a friend over to play, and they're talking about Beth, age 3]
Friend: "Your sister just said the word 'tropical.'"
Luke: "Yeah?"
Friend: "Yeah. She said the word 'tropical' and she knew exactly what it meant."
Luke: "So?"
Friend: "I think your sister is smarter than you."
Luke: "Oh come on, I know what 'tropical' means."
Friend: "Somehow she acts like she knows it better than you do."