Body language is probably more important in Thailand than it is in the West. Without expressing words, much can be conveyed in the type of smile a Thai person gives or the level of the wai when meeting somebody for the first time.
One common form of non-verbal communication is known in Thai as yak kiu. This is a gesture of confirmation or agreement which involves raising the eyebrows up and down (yak = move up and down; kiu = eyebrows). For example, if two friends are talking and one suggests to the other that they should go to the cinema to watch a movie, the other friend may yak kiu. The wiggly eyebrows are often accompanied with a slight smile which makes it even more endearing. As a non-Thai there’s no need to start practicing your yak kiu skills. A simple ‘yes’ or ‘OK’ will serve a similar purpose, but at least you’ll know what the deal is with the wiggly eyebrows if you notice Thai people doing it.