Back to a while ago.
Kain still maintained his lightning network, each [Thunder Bullet] appeared like a chain link of the network, just waiting for the Crawler to rush forward and activate.
Of course, Kain wouldn't protect himself too tightly either, because after a period of fighting, Kain had carefully observed and discovered that the behavior of these people was actually very intelligent, even compared to wild beasts. The pure desire to kill of the monsters was still there, but they also knew to seek benefits and avoid harm, not foolishly rushing forward to die in vain.
So within his electromagnetic net, Kain opened up passages that looked like gaps for the Crawlers to enter, giving them the impression that they had a chance of reaching him.
This is quite similar to the snake trap on the fifth floor of the Dungeon before.