Back in September 2012, a video was uploaded to youtube showing a pig rescuing a baby goat that was supposedly stuck in a pond at a petting zoo.
The video got millions of views on youtube and was widely aired in the media (including being shown on Good Morning America, the NBC Nightly News, and Fox News). Yesterday, it was revealed to be entirely staged.
It was created for a Comedy Central series, "Nathan For You," which is debuting this week (thus the timing of the reveal). The pig was directed toward the goat by means of an underwater plexiglass ramp.
The New York Times has a fairly long article about the video hoax, including comments from some media critics who take the news organizations to task for not questioning the video. Kelly McBride of the Poynter Institute says, "It really is embarrassing for the journalists who stumbled upon this and decided to promote it or share it with their audience. It's almost a form of malpractice."
Comedy Central has posted a follow-up video showing exactly how the original video was made.