  In a smooth family of projective, complex varieties, stable rationality need
not be preserved under generisation. This was proved by Hassett, Pirutka and
Tschinkel upon use of the specialisation method. Work of Schreieder produced
many more examples and introduced a simplification of the specialisation method
(no explicit desingularisation). In this text, I try to describe the combined
method from scratch in one of the simplest cases. A small, further
simplification consists in using specialisation of R-equivalence in place of
Fulton's specialisation for the Chow group of zero-cycles.
