The term IT SHAKES THINGS UP can be summarized by the crossword solution TREMOR, which is a 6 letter word. A TREMOR is an involuntary, rhythmic muscle contraction that causes shaking movements in one or more parts of the body. It is often associated with neurological conditions such as Parkinson's disease, essential TREMOR, and dystonia. Tremors can also be caused by stress, anxiety, fatigue, and certain medications.