Hm.... well for one, I can hear them talking most of the time--even at night if I wake up. They have conversations amongst themselves. I frequently wake up during the night and they are already talking, or singing some stupid song. They all like different things (we all have different favorite colors/songs/clothes/ food/ etc). They also look different when they are out so we are fairly easy to tell apart... and their voices are different for most of them. Also, I have an "inside world" where we can all see each other, and everyone looks very different (there are boys, girls, little kids, teenagers, a couple adults). Hm...also, we all act quite different.
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