MSMA (monosodium methanearsonate) is an arsenic-based grass killer. It kills grassy weeds such as crabgrass and goosegrass without harming most turfgrasses. It contains organic arsenic that, according to the University of Tennessee Extension, is less harmful than aspirin.
There are several styles of hearing aids available, from the smallest - Invisible in the Canal (IIC) to the largest and strongest - Power Behind the Ear (BTE), and the very popular Receiver in the Canal (RIC) - made to fit most hearing losses while remaining nearly unseen.
The type of presentation aids that speakers most typically make use of are visual aids: pictures, diagrams, charts and graphs, maps, and the like. Audible aids include musical excerpts, audio speech excerpts, and sound effects. A speaker may also use fragrance samples or a food samples as olfactory or gustatory aids.