How does this quote relate to a mysterious atmosphere?

Question

For one….Upon its head, with red extended mouth and solitary eye of fire, sat the hideous beast whose craft had seduced me into murder, and whose informing voice had consigned me to the hangman. I had walled the monster up within the tomb!” (Poe).

Ms. Sue · Answer

These words are scary. red extended mouth solitary eye of fire hideous beast What other words are scary?

T · Answer

seduced me to murder

Ms. Sue · Answer

Yep -- and more

T · Answer

but how does this make the atmosphere mysterious?

Ms. Sue · Answer

The words create a nightmarish feeling in me.