Mary is helping her son, Dean, put together a difficult, but manageable, puzzle. When Dean tries to insert a piece in the wrong place a few times, Mary points to the bottom of the puzzle and says, "Does it go down here?" Mary is engaging in

scaffolding

Explanation:

Scaffolding is a  method of instruction  in which teachers shows the process of solving a problem to the students and explain the steps as the students proceeds forward. After making a few  explanations, the instructor  then leaves students to work independently but help him only when he feels that is student is stuck and will need guidance. .

Here Dean was stuck while solving the puzzle and mary came to her rescue. This is clear example of Scaffolding

as university of miami psychologists debra lieberman and adam smith pointed out in a recent article in the journal current directions in psychological science, humans have social and psychological mechanisms to deter incest. with very few exceptions, marriages between brothers and sisters and between parents and their children are verboten in every human culture. the primary psychological anti-incest mechanism is the yuck response. even the idea of sex with their mom or dad, bro or sis is upsetting to most people. the psychologist jonathan haidt has found that nearly everyone is repelled by the prospect of brother-sister sex, even in hypothetical situations in which there is no chance of pregnancy).

the biological cost of incest

this raises an interesting question: just what’s so bad about incest? sure, having sex with your dad or your sister seems gross — but why? some anthropologists have argued that incest taboos are learned social conventions. this explanation, however, doesn’t make sense to me as it does not explain the widespread existence of anti-incest mechanisms in creatures ranging from cockroaches to chimpanzees. second, the incest taboo is about as close to a universal law as human moral rules get.

why should mechanisms to avoid incest be so widespread both in nature and across human societies? the answer is simple. the problem with having sex close with relatives is that there is an astonishingly high chance that your offspring will be born with a serious birth defect.