The title of this article is Monkeys Stay Away from Meanies. The article is about a study done on Capuchin monkeys where they showed the Capuchin monkeys different scenarios of people helping other people open a jar. Later, these people offered food to the monkeys. It turns out that the monkeys showed no preference to the people who helped open jars or were trying to open their own jars. The monkeys accepted food from either person. However, if person A refused to help person B open their jar, then the monkey tended to take food from person B when they offered food.
"The animals showed no bias against people who failed to help because they were busy opening their own jar. But they tended to avoid people who were available to help but did not do so."
The reason for this is that:
" “Explicit refusal to help is a signal that you’re dangerous, that you’re negative,” says Kiley Hamlin, a developmental psychologist at the University of British Columbia in Vancouver, Canada."
Listen to your mom, and don't accept things from strangers. :-)