Nilotic Anti-Swan

The Nilotic Anti-Swan (Anti-cygnus Nilus) is the opposite of a swan, and is indigenous to the Nile River.

Physical Properties
Anti-Swans superficially resemble swans and share several properties (monogamy, otherworldly grace, arm-breaking ability, ownership by the ruling monarch of England, &c.) However, according to prominent fake-cisist Agripinna Oakes, if ever a swan and an Anti-Swan were to meet, they would annihilate in a release of pure energy with obvious destructive consequences. For instance, some physical bunkeographers believe that the rift comprising the Nile river valley was formed during such an event.

Value of an Anti-Swan
There is a common misconception that the Anti-Swan is a lack of swans. However, this implies that if one was counting swans and came across an anti-swan, they wouldn't count it. Rather, they would count it as -1 swans. Likewise, a swan is -1 anti-swans.

Anti-Swans vs. Auntie Swans
Another frequent error is to mistake an anti-swan for a swan which is the sister of another swan's mother or father. This occurs chiefly in casual conversation or as a result of bad spelling, and has had historically tragic results when critical mathematical figures were involved (c.f.: the Leaning Tower of Swansea).