  Numerical approximations of shock waves sometimes suffer from instabilities
called carbuncles. Techniques for suppressing carbuncles are trial-and-error
and lack in reliability and generality, partly because theoretical knowledge
about carbuncles is equally unsatisfactory. It is not known which numerical
schemes are affected in which circumstances, what causes carbuncles to appear
and whether carbuncles are purely numerical artifacts or rather features of a
continuum equation or model. This work presents evidence towards the latter: it
is conjectured that carbuncles are a special class of non-physical entropy
solutions. Using a new technique for triggering a single carbuncle, their
structure is computed in detail in similarity coordinates.
