When I used to teach chemistry I always told my students a story about my mother to illustrate why you don't pipet by mouth. She worked in a biochemistry lab during college and had to digest rat livers in hydrochloric acid then pipet the digesstate onto flasks for dilution. One day she wasn't paying attention and aspirated an air bubble into the pipet and sucked a bit of the digesstate onto her mouth. She said it was gross to think about the rat liver, but having the acid strip the enamel from her teeth was worse.