Customs of different people are a big part of the book. What custom must Gulliver follow in Part 3, Chapter 9 and how, in general, does Gulliver deal with the customs of people he encounters?

In order to speak to the king, Gulliver has to crawl on his belly licking the floor, which is the custom. Gulliver does this and is treated well during his three-month stay in the country. That's not surprising at this point, since Gulliver has, generally, been treated well by people he encounters when he follows their customs. Swift is using this to explain that people are more likely to be respected when visiting foreign countries if they do their best to blend in.