As it went down, slipping lightly through the old man's fingers, he still could feel the great weight, though the pressure of his thumb and finger were almost imperceptible.
The short answer: new accents begin to develop when isolated groups of speakers start making nearly imperceptible changes to the way they pronounce words.
The flickering is so slight that it is imperceptible to the human eye, but the camera on another phone can detect it at a distance of up to ten metres.
Studies show the use of antiretroviral drugs dramatically reduces the risk of HIV transmission by lowering the amount of virus to near imperceptible levels.