Titus's mosquito/ a flea in one's ear/a bee in one's bonnet/"the gnat of Titus"

Figuratively: an obsessive, troubling, and irritating thought (from the story about the mosquito that entered Titus's brain).

("This is the wicked Titus, who blasphemed and reviled Heaven. What did he do? He took hold of a prostitute by the hand and entered the Holy of Holies, unfurled a Torah scroll, committed a transgression with it, and drew a sword and tore the curtain. A divine voice went forth and said to him: Wicked one, son of a wicked one, grandson of Esau the wicked! I have a small creature in my world, and its name is Mosquito... The mosquito came and entered his nostril and gnawed at his brain for seven years" - Gittin 56b; and likewise: "To gnaw at the brain, like the mosquito of Titus" - the Admor Menachem Mendel of Kotzk; and likewise: "He was amazed at himself that such a thing had come to his mind... He remembered the Talmudic passage in Gittin about the mosquito that entered Titus's brain and stabbed it ... but the mosquito inside him did not keep silent" - Chaim Sabato, K'Af'pei Shachar, 81)

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