Ushino koku mairi (paying a visit to a shrine at two o'clock in the morning to put a curse on someone) was an ancient magical ritual to break through the boundary that marks the sacred realm, to call upon a yokai and to use it in order to bring about misfortune upon someone against whom one has a grudge.
丑の刻参りも古くは神域の結界を破り、妖怪を呼び出し使役し、恨む相手に禍をもたらす呪術であった。