This idiot is Cadaverus! An here he is, in the finest Roman tradition, designated as a «volunteer» by his decurion to serve as a guinea pig for Valueaddedtax and Getafix, who must prove that they are real druids in order to obtain permission to travel to the forest of the Carnutes, where the Order of Druids is holding its prestigious annual meeting.
Cadaverus follows orders, and chews some of the herbs prepared by Valueaddedtax, the Belgian druid. The result is astonishing, because poor Cadaverus suddenly starts braying! This comes as a bit of a surprise, although not to his decurion, who declares «it hasn't made that much difference»!