Generate a question about the following movie plot: Young newlywed Marge Farrell (Gloria Talbott) notices that her new husband Bill (Tom Tryon) is acting oddly: He doesn't show any signs of affection towards her or anything else, including his pet dogs, which he used to love. Marge is also very concerned because she cannot become pregnant. She then notices that other husbands in her social circle are all acting the same way. One night, she follows Bill while he goes for a walk. She discovers that he is not the man she married but an alien impostor: An extraterrestrial lifeform leaves his human body and enters a hidden spaceship. She confronts Bill, and he eventually explains that all the females on his planet are now extinct, and that he and other males of his species are taking over human men so they can mate with Earth's women, saving their race from extinction. Marge is horrified at this prospect and tries to warn others of this alien plot, but too many men in town have already been taken over, including the town's Chief of Police. Finally, her doctor (Ken Lynch) comes to believe her wild story, and he gathers up a posse to attack the aliens in their hidden spaceship. Although bullets can't hurt the invaders, they are defenseless against a pair of German shepherd dogs being used by the posse; eventually, all the aliens are killed by the dogs. Entering the spaceship, the posse finds all of the human captives still alive, including Bill. Shortly thereafter, a fleet of spaceships is seen taking off from all over the world; the aliens must seek females elsewhere, now that their breeding plan on Earth has been discovered.
The answer to this question is:
What can't hurt the invaders?