"If a tree falls in a forest and no one is around to hear it, does it make a sound?" is a philosophical thought experiment that raises questions regarding observation and perception. == History == While the origin of the phrase is sometimes mistakenly attributed to George Berkeley, there are no extant writings in which he discussed this question. The closest are the following two passages from Berkeley's A Treatise Concerning the Principles of Human Knowledge, published in 1710: But, say you, surely there is nothing easier than for me to imagine trees, for instance, in a park, or books existing...

A click farm is a form of click fraud where a large group of low-paid workers are hired to click on links or buttons for the click fraudster (click farm master or click farmer). The workers click the links, surf the target website for a period of time, and possibly sign up for newsletters prior to clicking another link. For many of these workers, clicking on enough ads per day may increase their revenue substantially and may also be an alternative to other types of work. It is extremely difficult for an automated filter to detect this simulated traffic as fake because the visitor behavior appears...