One Difference (among the multitude) between a Human and two, maybe three, Monkeys

An old but venturesome female Colobus Monkey, named Tweedle Dee, one day left the forest and ventured into human habitat. It chanced upon a shining mirror in a public bathroom. It pointed to the mirror and said, "Ha, ha, ha, you're an old, ugly monkey. " The image in the mirror pointed the finger back at the monkey at the same time a voice echoed in the tile-walled enclosed bathroom, "Ha, ha, ha, you're an old, ugly monkey." Frightened, it sought refuge underneath the sink, all shaken with fear and defecated and urinated on the floor, stinking the place.

Another ancient female monkey walked in. Its name is Tweedle Dum. It is a Pygmy Marsoset. It also saw itself in the mirror, uttered the same remark, hid underneath the sink, and shit and pissed on the floor exactly like the other monkey did. 

A female aged, decrepit bonobo walked in. It recognized itself in the mirror. It said nothing. It tried to squeeze some pimples off its wrinkled, weather-beaten face.

A handsome, virile, tall, athletic, middle-aged human male walked in. He saw the bonobo. He came over and knocked on its head, "Is anybody home?". A resounding empty sound came back. The man smiled and said, "Just as I thought. Empty-headed. Your skull is an empty vessel, devoid of thoughts." He then saw the two monkeys trembling and clinging to each other underneath the sink. He said, "You two look familiar. What are you doing here? You two should be back in the dark jungle where you belong."