Answer: Black magic

In February of 1941, residents of Central Europe and immigrants from that area residing in Washington, D.C., called upon the old pagan deity of Istan (akin to the Magyar or Hungarian word Istvan for god) to invoke his wrath to effect Hitler’s demise. Illustrations and even cardboard cutouts of a skeletal figure representing Hitler, along with wooden dolls, were stuck with pins in vital organs in the belief that the mass murderer would thus suffer destruction.

And not to be left out, the group's cat made sure he was involved, seen above "examining" a Hitler voodoo doll!

During World War II, supernatural customs were still prevalent in Europe, and they were sometimes used to afflict nefarious characters, such as Adolf Hitler, with disease or death. These photographs, found within HSP's Philadelphia Record photo morgue, reveal that the belief in “image magic” persisted at that time.

You can see the original photographs featured here in the Philadelphia Record morgue collection (#V07), which also contains many images pertaining to local actions during and reactions to World War II.