Clove of garlic
Priests start with cloves of garlic in their inventory, and it also occasionally generates randomly.
Undead and garlic
No undead except ghosts and shades will enter a square with a clove of garlic on it. However, placing garlic on a stairway does not prevent covetous undead, such as master liches, arch-liches, or Vlad the Impaler, from warping to it.
According to Central European folklore, garlic can ward off vampires, werewolves and demons.
1 November - All day long we have travelled, and at a good speed. The horses seem to know that they are being kindly treated, for they go willingly their full stage at best speed. We have now had so many changes and find the same thing so constantly that we are encouraged to think that the journey will be an easy one. Dr. Van Helsing is laconic, he tells the farmers that he is hurrying to Bistritz, and pays them well to make the exchange of horses. We get hot soup, or coffee, or tea, and off we go. It is a lovely country. Full of beauties of all imaginable kinds, and the people are brave, and strong, and simple, and seem full of nice qualities. They are very, very superstitious. In the first house where we stopped, when the woman who served us saw the scar on my forehead, she crossed herself and put out two fingers towards me, to keep off the evil eye. I believe they went to the trouble of putting an extra amount of garlic into our food, and I can't abide garlic. Ever since then I have taken care not to take off my hat or veil, and so have escaped their suspicions.