If they look back at the coffin, they will notice that both the apple and the lemon cake have disappeared (and a strange humming in a certain tune occurs, very silently but they can hear it if they try) as the coffin disappears.

They find another very horrible hallway, with different sort of poisonous barrels on the ground. However, Rinku's garlic necklace protects them from the poison that seeps into the air.

At the same time, the silver dagger Eren is carrying starts glowing an eerie red light. Behind the corner they find a demon. Due to Eren having the dagger the demon takes his form. Any damage done to the demon reflects back to Eren and reduces his hearts. Any fatal damage done to the demon will take all of Eren's hearts (if this happens, let me know).

Even if Eren would throw the dagger away, the effect doesn't go away anymore.

Using a flashlight at him will null this effect as it reveals the demon's true form (which is just a ugly creature with leather like wings and sharp fangs).

They need to deal with the demon in order to proceed.