Muscle twitching is caused by minor muscle contractions in the area, or uncontrollable twitching of a muscle group that is served by a single motor nerve fiber. Muscle twitches are minor and often go unnoticed. Some are common and normal. Others are signs of a nervous system disorder.
Yerba mate has a slight astringent bitter taste due to the high tannin content of the leaves. Researchers have found that leaves from younger plants possess more tannins than leaves from older, more mature trees.
Black tea contains tannins but not tannic acid. Like fine wines, teas -- especially black teas -- are often described by tasters as tannic.. This means they contain high levels of certain phenolic flavor compounds, collectively called tannins, that give the tea its refreshingly astringent, slightly bitter taste.