 Intuitively, the basic idea is that (in the overdetermination case) the ‘most normal’ value of each of BT and ST is 0 (throwing rocks at bottles isn’t normal!), so from the perspective of a world where ST = 0, BS counterfactually depends on ST (and similarly for BT). So both Billy’s and Suzy’s throws count as causes of the bottle’s shattering. Poisoning someone’s coffee is also not normal. So we hold Killer’s failure to poison the coffee fixed (so in this case the ‘most normal’ world is just the actual world as far as the poisoning is concerned), which delivers the right result that Victim’s survival does not counterfactually depend on Bodyguard’s administering the antidote. (See Hitchcock 2007 for a different solution that trades on the default/deviant distinction.)