The 'harisen' is a giant folding fan which is usually made to appear closed, and is used by a straight man (tsukkomi) in a Dotsuki manzai (comic backchat using a tap as an interjection.)
大きな紙を折り畳んで一方をテープで止めたものは、「ハリセン」と呼ばれ、ドツキ漫才などでツッコミ用に使われる。