1810, member of a gang of murderers and robbers in India who strangled their victims, from Marathi thag, thak cheat, swindler, Hindi thag, perhaps from Sanskrit sthaga-s cunning, fraudulent, possibly from sthagayati (he) covers, conceals, from PIE root *(s)teg- cover (see stegosaurus).
It may also occur in one ear or both ears. The most common reason for muffled hearing is conductive hearing loss that can be caused by a variety of factors or medical conditions including a build up of ear wax and ear infections. In most cases, however, it is treatable and does not lead to permanent hearing damage.
I second the first comment. I am a Labor and Delivery nurse. I use fetal monitors every day. And the reality is that the scientific evidence shows that fetal hear monitors do not help mothers or babies. Since the beginning of their use, maternal and fetal outcomes have not improved at all. In fact, they may have hurt.