Answer: Chicken Heads

Starting around the mid 20th century, rabies was slowly working its way from eastern Europe across the continent via infected red foxes. Unlike many other zoonotic diseases, rabies is a serious threat as it requires immediate and costly medical intervention or the disease is fatal (only a few individuals have ever survived rabies without the vaccine shots thanks to treatment using the Milwaukee Protocol).

Given the danger, European countries have invested significant amounts of money and time over the years in combating the spread of rabies in the fox population. Many of the early attempts proved unsuccessful or were so costly as to be unsustainable. Capturing animals and vaccinating them was effective but impractical. Hunting and exterminating all of the foxes was unsustainable and required too many man hours with too little return. Vaccine traps worked but, again, were costly and difficult to deploy in wide enough areas.

Ultimately, the solution that worked (and was in continual use until the early 1990s before being replaced by mass-produced tablets of fish or fat) was disarmingly simplistic. Rather than go to great lengths to locate the foxes and manually vaccinate or exterminate them, the teams in charge of managing the rabid fox population started air dropping chicken heads with capsules of vaccination fluid embedded under the skin. The foxes would naturally seek out the treat, gobble it up, and in the process consume the oral vaccine. The method proved so effective that the incidence of rabies across Europe dropped significantly. Typically within 5-10 years, the incidence of rabies would drop in a treated region by 90 percent or more.