Sometimes, it's really hard to understand a person's thought process, especially when you know they're not just pretending to be crazy or stupid in front of you.
Mr. Su Bai knew Emma was speaking the truth; she wasn't joking or pretending anything.
From the first time he met Emma in the previous story world, seeing her holding a male audience member's hand and asking him if he wanted to eat it, Mr. Su Bai could feel a kind of sincerity.
Actually, Mr. Su Bai was also aware that he and Emma were alike; both were very sincere, neither wanting to go against their own desires and do something they were unwilling to do.
Everyone has moments when they show their sincere side, just like now, Mr. Su Bai absolutely believed, if he were to undo his belt now, Emma would very devotedly use her mouth and chest to serve him, and then after he had his pleasure, she'd bite off and eat his root in one gulp.