Figure 3. The cage-in-cage system used for the predator stress procedure, which consists of a large outer cage for the predator (cat) and a small inner cage for the prey (mouse).

Both cages were made of steel-wire mesh; while the large cage measured 100 cm in length, 50 cm in width and 40 cm in height, the small cage measured 19 cm in length, 13 cm in width and 12 cm in height. The prey cage was fixed in such a position inside the predator cage that the cat and the mouse could see each other clearly from at least three sides.