The microscope is the most important advancement.<span />
The mouth is where the food is digested first, saliva is released to break down the food, and teeth break up the food
Some stimuli act as attention-getting stimuli due to their physical characteristics; others, due to their meaningfulness, act as attention-holding stimuli.
For example, somebody's physical appearance, of a person who is attractive, is used as an attention-getting stimuli, but their psychological qualities are what hold your attention due to their meaningfulness.
