The Dursley Household in the Summer Before Fifth Year

While away at school, Dudley had come across a genuine magical hypnosis pocket watch. He had tested it on a couple of his friends saying he was trying to learn. Once he had gotten them under his control, he told them to give him some of the money in their wallets and forget about it.

During his testing, he found out that while he could hypnotize people in as many hypnotism sessions times as he wanted and have them do as he says when they’re under his control, the watch could only giving three commands that would last when the hypnotism ended per day, before the watch would lose its hypnotic effect.

Once he knew that his hypnosis really worked, he knew exactly what he was going to do. Getting home from school before Harry did, Dudley decided to make use of his time and get his parents under control.

Once he had out his things away he told them he wanted to show them something he had leaned. From what he figured out at school the weaker willed someone was the shorter amount of time it took to get them under control. However, as long as they looked at the hypnotic pocket watch for long enough then the person would follow his orders.

“Mum, dad, look, I want to show you a slight of hand trick I learned at school,” Dudley boasted.

“Oh, I’m so proud of you dudders,” Petunia tutted. “That’s my boy,” Vernon said proudly.

“See,” Dudley pointed at the magical pocket watch he’d taken out of his pocket, “All you need to do is look at this while it swings.”

Swinging the pocket watch slowly, Dudley’s parents follows it with their eyes. After enough time had passed, their eye’s had started swirling, showing they were hypnotized.

Intoning importantly, Dudley spoke, “You won’t notice anything strange going on this summer, if you think you see something strange, that has to do with magic, or people who use magic, you will ignore it and forget it.”

Once his parent’s eyes flashed black, he the command took hold.

Excitedly, Dudley ordered, “When Potter comes back from school, you're going to tell him to sit in the living room and tell him it’s so I can practice something I learned at school with him.”

When his parent’s eyes flashed black again, Dudley stoped swinging the pocket watch and saw his parents eyes stop swirling showing they were falling out of the trance and said, “See, wasn’t that really cool!”

“Of course, of course,” his parents said, even though they didn’t understand what he was excited about.