A "tremor" refers to an involuntary shaking or quivering movement, usually in your hands, legs, or other parts of your body. It can be a result of different causes, such as anxiety, nervousness, or certain medical conditions. Full definition
A recent example was the series of tremors of magnitudes 2.01 - 2.55 that occurred in Mariana, Minas Gerais state, three days before the collapse of the Fundão tailings dam owned by Samarco, resulting in the worst environmental disaster in Brazilian history. (sciencedaily.com)
Sometimes some Australian Shepherds will have involuntary muscle tremors in the hindquarters. (ashgi.org)
High levels of theobromine (theobromine poisoning), can cause muscle tremors, seizures, an irregular heartbeat, internal bleeding, and / or heart attack. (stewartpet.com)