The standard economic model of bilateral precaution postulates an interdependency between the care taken by injurers and victims that operates through the effects of each on the expected accident loss. This paper considers situations in which each party's precaution affects not only expected accident loss, but also directly affects the other party's cost of taking precaution. Generalizing the economic model of tort law in this way allows for a more complete analysis of when standard tort rules can and cannot induce optimal precaution. When this additional externality is introduced into a model of unilateral harm (where all accident losses are borne by the victim), none of the standard tort liability rules induces socially optimal behavior by both parties. Moreover, under a contributory negligence rule, the only equilibrium is in mixed strategies; this gives rise to the possibility of litigation in equilibrium. A 'tort-like' liability rule that induces socially optimal behavior by both parties is then characterized; this involves a payment by victims to non-negligent injurers whenever an accident occurs. The model is then extended to consider the case of bilateral harm (where both parties suffer accident losses). It is shown that, as long as both parties can sue to recover their accident losses, all negligence-based tort rules lead to socially optimal behavior by both parties.