Fly
From Tardis Wiki, the free Doctor Who reference
Flies were non-sentient insects native to Earth. Barbara Wright and Ian Chesterton encountered a fly when they were miniaturised in 1960s England. Although flies were ordinarily of insignificant mass to humans, this particular fly was a genuine threat to Barbara and Ian. Fortunately for them, it lit upon something coated with the insecticide DN6 and died. (TV: "Dangerous Journey")
