Ellie is shocked to find that in comparison to Annie, she's a perfectly sociable and normal human being. HOW DOES THAT HAPPEN EVEN WHAT IS THIS WHY IS THIS CHILD SO PRICKLY. All Ellie's weird qualities - cageyness, connecting to people best through violence, bluntness, etc etc - are all so much more pronounced in Annie that it's almost distressing for her to see. Especially since Annie is just sixteen, and when Ellie was sixteen she was a much happier person.

Annie, on the other hand, gets a brief pang of jealousy before her lack of imagination catches up with her and she can't actually accurately picture what it would be like to grow up in a world with no child soldier bullshit. She proceeds to Annieface at Ellie's careful probing and attempts to be "nice" (haha) until Ellie asks to see the Female Titan. Annie obliges - YAAAY SHOWING OFF YAAAYYY - and later they fight each other for funsies. Annie wins.