What are "Entresijos" and "Gallinejas"?

We've recently had in Madrid the festivities in honor of its patron saint "San Isidro" (which official day is May 15th). They're celebrated in the "pradera de San Isidro" (medow), where you can find many food stalls and fairground rides. Two of the most traditional foods in Madrid are "Entresijos" and "Gallinejas", and they can be found almost in every stall there these days.
But what are they? Find it below!