  We make further observations on the features of Galois cohomology in the
general model theoretic context. We make explicit the connection between forms
of definable groups and first cohomology sets with coefficients in a suitable
automorphism group. We then use a method of twisting cohomology (inspired on
Serre's algebraic twisting) to describe arbitrary fibres in cohomology
sequences -- yielding a useful finiteness result on cohomology sets.
  Applied to the special case of differential fields and Kolchin's constrained
cohomology, we prove that the first constrained cohomology set of a
differential algebraic group over a bounded, differentially large, field is
countable.
