The main Idea of the chapter is that weird things have been going around the Dursley's and people are talking about the Potter's. Mr. Dursley saw a cat reading a map. He saw people cloaks. When he was at work he heard people talking about the potters. He also saw owls during the day.
The main idea of the chapter is it is Dudley's birthday, they went to the zoo and a snake escaped the zoo. It was Dudley's birthday and they went to the zoo and Harry had to come with. When they went in the reptile house Harry started to talking to the snake then Dudley and his friend came back and the glass vanished and the Boa Constrictor escaped to Brazil.