An 'Osei-chu' (mimicking roundworm) or 'Osei' (literally, mimicking or parroting the host's words) is a weird disease or a ghostly roundworm which causes the disease known in China and Japan, as described in collected essays written in the Edo period, such as "Shin Chomonju" (literally, a new collection of famous tales) and "Kanden jihitsu" (literally, fallow-field essays, continued; miscellaneous essays).
応声虫（おうせいちゅう）または応声は、中国や日本の『新著聞集』や『閑田次筆』などの江戸時代の随筆集にある奇病、及びその病気を引き起こす怪虫。