What you are looking at are memories. In this case containing to one individual....

Albus Dumbledore: [to Harry] What you are looking at are memories. In this case containing to one individual. Voldemort. Or as he was known then, Tom Riddle. [takes a memory] Albus Dumbledore: This file contains the most particular memory. The day I first met him. I'd like you to see it. If you want. [Harry takes the memory, poors its contents into the Pensieve, puts his head in the Pensieve, and watches Mrs. Cole leading a younger Dumbledore to Tom Riddle] Mrs. Cole: I must admit to some confusion receiving your letter, Mr. Dumbledore. In all the years Tom's been here he's never had a family visitor. There have been incidents with the other children. Nasty things. [knocks on Tom Riddle's door and opens it] Mrs. Cole: Tom, you have a visitor. Albus Dumbledore: How do you do, Tom? Tom Riddle - Age 11: Go. [Dumbledore seats himself] Tom Riddle - Age 11: You're the doctor, aren't you? Albus Dumbledore: No. I'm a professor. Tom Riddle - Age 11: I don't believe you. She wants me looked at. They think I'm... different. Albus Dumbledore: Well, perhaps they're right. Tom Riddle - Age 11: I'm not mad. Albus Dumbledore: Hogwarts is not a place for mad people. Hogwarts is a school. A school of magic. [a puzzled expression comes across Riddle's face] Albus Dumbledore: You can do things, can't you, Tom? Things to the children, Tom. Tom Riddle - Age 11: I can make things move without touching them. I can make animals do what I want without touching them. I can make bad things happen to people who are mean to me. I can make them hurt. If I want. Who are you? Albus Dumbledore: I'm like you, Tom. I'm different. Tom Riddle - Age 11: Prove it. [Dumbledore conjures a fire in the wardrobe] Albus Dumbledore: I think there's something in your wardrobe that's trying to get out, Tom. [Riddle opens the burning wardrobe and finds a small box rattling, while the flames disappear] Albus Dumbledore: Thievery is not tolerated at Hogwarts, Tom. At Hogwarts you will not only be taught how to use magic, but how to control it. Do you understand me? [leaves] Tom Riddle - Age 11: I can speak to snakes, too. They find me... whisper things. [Dumbledore turns around] Tom Riddle - Age 11: Is that normal for someone like me? [Dumbledore looks at Riddle and Harry suddenly takes his head out of the Pensieve]