There was a fearful scream which almost froze our hearts to hear. As he had placed the Wafer on Mina’s forehead, it had seared it – had burned the flesh as though it had been a piece of white-hot metal.
– Bram Stoker
Dracula, Chapter 22. After Mina is bitten by Dracula, Van Helsing places a Holy Communion wafer on her forehead and it burns her and leaves a bright red scar. The Communion bread is a symbol for the body of Christ and is used to repel vampires.