The term 'kind of reaction' can refer to a variety of different reactions. GUT is a 3 letter word that refers to an instinctive or intuitive reaction, such as a GUT feeling. ALLERGIC is an 8 letter word that refers to an immune system response to a foreign substance, such as pollen or dust. CHAIN is a 5 letter word that refers to a series of reactions, such as a CHAIN reaction. DELAYED is a 7 letter word that refers to a reaction that is not immediate, but rather occurs after some time has passed. KNEEJERK is an 8 letter word that refers to an automatic or reflexive reaction, such as a knee jerk reaction.