|This might be|
|But we're not sure|
A hoax is an intentionally perpetrated fraud, as opposed to a misunderstanding, mistake, or even exaggeration over time. Usually, a hoax implies an outright lie with the evidence entirely invented from scratch.
 In science
Scientists are, admittedly, human and therefore prone to the lapses in judgement that cause them to create hoaxes. In the context of science, hoaxes are intended to either bring fame to otherwise unknown scientists, to discredit another scientist or theory, or to provide "proof" of something that "we just know is right". Science loathes hoaxes, and spends significant resources disproving them, even if the hoax actually adds weight to a desired argument. Some hoaxes perpetrated within the scientific community include the Piltdown Man and the Tesaday Tribe.
Christian fundamentalists, in attempting to discredit science often bring up the Hoaxes that have been promulgated by scientists (including the non-hoax "exaggerations" of Haeckel). What they fail to mention is that every single hoax they know of was found and disproven by other scientists who said "wait, this doesn't make sense".
 Hoaxes of exposure
Some hoaxes have been deliberately launched in order to shame or expose credulity or folly of various sorts. The Sokal affair, in which a paper purporting to be about quantum physics that actually claimed that all reality was a social construction, was published in a non-peer-reviewed journal dedicated to postmodernism, was one such hoax. The Taxil hoax was another, meant to discredit the Roman Catholic Church's campaign against Freemasonry. Other such hoaxes include Disumbrationism, in which various bizarre daubs were displayed with pretentious commentary as modern art, and Spectra: A Book of Poetic Experiments, doggerel meant to masquerade as modernistic poetry.
 Fundie interpretation of the above
Fundamentalists like to deny everything about scientific authority, so they are adamant about emphasizing all scientific hoaxes of the above kind, even after "science" itself has disproven the hoax and distanced itself from--if not disowned--the hoaxsters. Using the fact that some hoaxes have been perpetrated in the past, fundamentalists like to suggest that many fully accepted archeological, biological, and other scientific finds are also hoaxes, causing people to doubt scientific authority.
 Non science hoaxes
Urban mythology, New Age studies, cryptozoology, and extraterrestrial obsessions struggle to exist on the fringes of science, and hoaxes are often employed to bring more people into the fold. Hoaxes can be widely believed for a long time if they are done well enough. Some famous examples include:
- Cottingley Fairies: Two young girls fake photographs of fairies, fooling most of the media (and well known nutbag spiritualist Sir Arthur Conan Doyle), for several decades. Even after admitting to them being faked may years later - and explaining the methods- some still believe they're real.
- Crop circles: Although reports of these have gone back a while they shot to prominence in the 1970s. Their original creators have admitted to the hoax and crop circle making is now a competitive sport in some... erm, circles.
- Loch Ness Monster: The most famous photograph of the monster, taken in the 1930s, was revealed to be a hoax by its creator. It's actually cropped down considerably to give the illusion that the monster is much larger, the full photograph clearly shows that it's actually tiny.
- The Fox Sisters claimed to be receiving messages from the dead - and invented Spiritualism which is still fleecing the credulous to this day.