Faeces
Faeces was solid or semisolid waste produced by several species in the process of defecation. It typically consisted of food components which could not be digested, and thus were expelled from the body. (PROSE: The Dying Days)
In 1599, residents of Southwark dumped buckets of faeces and urine out of their windows, as indoor plumbing was not yet widespread. To warn passersby, the residents would shout "Gardez l'eau!", French for "Watch out for the water!". Martha Jones and the Tenth Doctor encountered such a situation on their first adventure together. Although they narrowly avoided being hit, the Doctor still felt obliged to apologise. (TV: The Shakespeare Code)
In 1814, Lord Sutcliffe employed dredgers to collect the faeces of a sea serpent under the River Thames. It was said to burn longer and hotter than coal, along with being able to burn underwater. Sutcliffe kept the serpent captive in order to continue harvesting the faeces. (TV: Thin Ice)
Another encounter with the faeces of sea creatures occurred in 2009. Whilst under the Severn Bridge, Gwen Cooper saw what she referred to as a "carpet of grey stuff", which was later revealed to be fish faeces. Carlie noted that this substance was often referred to euphemistically with the phrase "marine snow". (AUDIO: Submission)
Many considered the stench of faeces overpowering. (PROSE: The Pit) However, some species, such as Tritovores, ate the faeces of other species to survive. (TV: Planet of the Dead) The Tenth Doctor noted to Christina de Souza that this was "perfectly natural" to them, indicating a cultural divide between Tritovores and humans of her time.
Whilst travelling on The Motorway of New New York, Cheen and Milo recycled "all waste products" into food, including faeces. They offered Martha a biscuit made from this waste, which she promptly discarded upon learning of its composition. (TV: Gridlock)
