Needle

The First Doctor reflected that looking for a needle in a haystack would be simplicity itself compared to his task of locating the source of a distress call amongst the Zarbi's anthills. (PROSE: The Lair of Zarbi Supremo)

The Eleventh Doctor conceded that looking for a Weeping Angel among statues was like looking for a needle in a haystack if the needle looked like hay, "a hay-alike needle of death in a haystack of [...] statues." (TV: The Time of Angels)

Some people had a fetish for needles. (TV: Reset)

When the Eighth Doctor said that he would look into the history of Calcot to try to find why the TARDIS had landed there, Liv Chenka sarcastically said that she would try to find a needle in a haystack. (AUDIO: Absent Friends)