Think about all the people you know and what it is about their personalities that stand out to you. I’ll bet in at least some cases, your answer is based on how they speak. For example, the guy at the office who uses a certain phrase all the time, or the lady who lives down the block who always seems to be chomping on a stick of chewing gum and cracking it in between sentences. Or maybe you know someone sarcastic—always saying one thing but meaning another, in a mean or nice way. Or you have an uncle who is always cracking jokes, or an aunt who talks veeeeerrrrryyyy slooooowly. These types of characteristics make a person unique and memorable. The same applies to characters in a book.