i think the whole process from page 1 to page 3 is a waste of time , instead of making fake heads for every single customers , the brothel can just use 1 single mold to mass-produce the same head for every customers beforehand .
the real head of the current customer is hidden , so the mantis girl doesnt know the real head of the customer , so she can just eat the brothel 's basic head instead of the fake head of the current customer .
and the customer can only see the girl eating something , he cant see that his fake head is being eaten .
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fun fact : there are some henta* about mantis girls , lol .
i bet that a mantis girl 's blowjob and handjob must be very horrible , lol .
i guess you can say : a dullahan is always "losing their head" , lol :
lose one's head = (idiomatic) To behave irrationally or to lose one's self-control, especially in a distressing situation .