Reactions are a selection of expressions used in Animal Crossing New Horizons obtained through talking to villagers on your island. initially, after a couple days of starting a new island, a default of four reactions are given to the player character. Every day after that, a new reaction can be taught randomly out of a pool of 40 different reactions, outside of special event reactions. Each villager personality type can offer five different reaction, with the fifth reaction given only when best friendship has been reached. It is heavily suggested to have one of each type of villager on your island to unlock all 40 reactions in the game.
Note: Reactions denoted by * require best friendship with that villager personality type.
Special Event Reactions are given through free update events usually commemorating an in-game holiday or event. They are obtained either by talking to your villagers, through the Nook Stop or through Nook's Cranny.
Halloween Reactions: Both reactions are obtained Halloween night by one of your villagers. Haunt Scare