You stick horns in the ground using them as spikes and you line up the horns in a straight line. Horns are pretty much the same thing as spikes once you stick them in the ground, and you line these ones up precisely for optimal protection.
As you line up these horns and stick them into the ground, you notice a bull munching on hay (へい) nearby. It's staring at the horns you're lining up. Somehow it feels like it's munching that hay angrily. You gulp, looking at its horn as it grabs another mouthful of hay, and you feel pretty guilty.