Why does Ralph send Abby into his mother's basement and close the door in the novel, Motherthing?

Early on in the novel, shortly after Laura's passing, Ralph claims that Laura is still alive and can be found in the basement of the house. Abby goes down there and Ralph shuts her in so she can see her, and Abby hears some bumping noises but ultimately does not quite believe that Laura is down there. For Ralph, it is a different story entirely. He hears her talking to him and asking him to cut himself to give her his blood.