Rats pressed a lever to avoid shock on a free-operant avoidance schedule. Some subjects were also exposed to extinction in which the response-shock contingency was eliminated while the shock-shock contingency remained in effect. A specially constructed lever was used that registered not only presses, but also biting attacks on the lever. Throughout various phases of the study, shocks often elicited lever biting as well as post-shock responding. The results suggested that shock-elicited attacks that are forceful enough to activate the operandum might account for some of the responding that occurs in experiments on free-operant avoidance behavior. In particular, shock-elicited operandum attacking might account for post-shock response bursting during free-operant avoidance and the extreme persistence of responding sometimes noted when shocks are delivered during the extinction of avoidance behavior. To the extent that this is true, these phenomena should not be characterized as operant behavior in interpreting the results of experiments on free operant avoidance.Aversive stimuli can cause animals to attack other organisms and inanimate objects. For example, O'Kelly and Steckle (1939) and Ulrich and Azrin (1962) found that when painful electric foot-shock is delivered to paired rats, a stereotyped fighting reaction results. This attacking occurs almost immediately after a shock presentation, and is therefore said to be elicited by the shock. Ulrich and Azrin (1962) were not able to demonstrate shockelicited attack by freely moving rats towards inanimate objects (a small doll and a stationary dead rat); however, Azrin, Rubin, and Hutchinson (1968) obtained reliable biting attacks towards metal, wood, and rubber targets when the rat was forced to face the target and was close to it.Azrin, Hutchinson, and Hake (1963) found that shock will elicit fighting in squirrel monkeys, and Azrin, Hutchinson, and Sallery (1964) showed that squirrel monkeys, when shocked, will attack not only other monkeys, rats, and mice, but also a stuffed doll and a cloth covered ball. Moreover, Hutchinson, Azrin, and Hake (1966) demonstrated that