Context. The carbon-rich asymptotic giant branch star IRC+10 216 undergoes strong mass loss, and quasi-periodic enhancements of the density of the circumstellar matter have previously been reported. The star's circumstellar environment is a well-studied and complex astrochemical laboratory, in which many molecular species have been proved to be present. CO is ubiquitous in the circumstellar envelope, while emission from the ethynyl (C2H) radical is detected in a spatially confined shell around IRC+10 216. We recently detected unexpectedly strong emission from the N = 4-3, 6-5, 7-6, 8-7, and 9-8 transitions of C2H with the IRAM 30m telescope and with Herschel/HIFI, which challenges the available chemical and physical models.