Gu Mian suspected that whatever had just knocked on the door might be able to turn invisible, and that right now it was very likely already out of the door.
Although when he opened the door just now he had only opened a small crack, and he'd been blocking that crack himself, so for the ghost to get out it would have had to knock him aside. But the greenhouse's main door here was very tall, and there was no guarantee the ghost hadn't crawled out through the gap above his head.
So he wanted to use Keke's Money Can Make Ghosts Grind to lure out that possibly invisible ghost.
"Got it on me," Keke answered. "You want me to take it out and use it right now?"
"Use it."
Keke nodded, then took a gigantic millstone out of her inventory.
The millstone hit the ground with a heavy thud that made the floor tremble a few times, and several ghost models nearby toppled over from the shock.
