In certain instances animals attempted to avoid shock by grounding themselves. As in Watson’s early finger avoidance study (1916), electrical continuity is only maintained if the rat is in contact between two electrodes or, in our case, two electrified bars comprising the grid floor of the operant chamber. Occasionally, animals balanced their hind paws on a single bar while propping their front paws on a side of the operant chamber, thereby breaking the continuity of the electrical circuit and avoiding footshock.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3675318/