The Luxo Ball is a recurring easter egg seen in nearly all Pixar movies.
During the scene where one Army Man gets injured and has to be helped by another soldeir into a flower pot for them to hide in, while dragging the wounded soldier to the pot a couple of children kick a Luxo Ball down the hall, almost hitting the soldiers.
After Andy opens Buzz Lightyear him and his friends rush off to Andy’s bedroom to play with his new toy. While passing the flower pot we can see one of the children dribbling the Luxo Ball and shortly afterwards, dribbling the ball into Andy’s room once they burst the door open.
When Woody challenges Buzz to show everyone he can fly, Buzz jumps off of Andy’s bed and bounces off of the Luxo Ball on the floor which sends him “flying” around the room.