After they declare Joey their favorite Friend, Aniston shows herself and they scream, truly scared.
But, then they both stop briefly, realize who has scared them, and the woman in the yellow t-shirt begins screaming again.
Then, we have the next duo, who win in my book for best overall screaming.
It must have freaked Jennifer Aniston out, because she finally gave up and said that Joey is her favorite, too, as Yellow Shirt looked on with a truly pained expression on her face.