Pinel, J. P., & Treit, D. (1978). Burying as a defensive response in rats. Journal of Comparative and Physiological Psychology, 92(4), 708-712.
95 naive adult male hooded rats tested in the presence of bedding material incorporated it into a striking behavioral sequence. Ss shocked once through a stationary prod buried this shock source, even when the shock-test interval was 20 days. Moreover, the burying seemed to be guided specifically by the relation between the prod and the shock; Ss shocked through a grid did not bury the prod, and Ss shocked by 1 of 2 identical prods buried only the shock prod.
Pinel, J.P.J. and Treit, D. (1979) Conditioned defensive burying in rats: availability of burying materials. Animal Learning and Behaviour, 7, 392-6
Rats shocked once by a stationary, wire-wrapped prod mounted on the wall of the test chamber incorporated sand, wooden blocks, or commercial bedding material on the floor of the chamber into a defensive response. They moved the available material toward and over the shock prod in all three conditions, adapting the response topography to the particular demand of the available material. In the sand and bedding conditions, the rats buried the prod by pushing and spraying piles of the material with snout and forepaws, whereas, in the blocks condition they picked up the blocks with their teeth and placed them individually around the prod. In Experiment 2, the rats buried the shock prod with blocks even when they had to first carry the blocks to the prod from the back of the chamber. Thus, conditioned defensive burying is not a simple, reflexive response to objects paired with a painful stimulus: it is a complex behavioural sequence that can vary as a function of the availability of burying materials.