A sudden burst of activity is a phenomenon that can be described by three words: FLURRY, RUSH, and SPASM. A FLURRY is a sudden, brief burst of activity, often involving a lot of movement. A RUSH is a sudden, intense burst of activity, usually involving a lot of energy. A SPASM is a sudden, involuntary burst of activity, often caused by a reflex. All three words describe a sudden burst of activity, but each word has its own unique connotation.