The Brewster’s cellar in Arsenic and Old Lace is the source of the sisters’ biggest secret, and this idea applies to all characters with something to hide. Characters only visit the cellar when they are attempting to keep a secret: the sisters visit the cellar to bury victims and hold funerals, Teddy unknowingly uses the cellar as a means of aiding his aunts in their murderous hobby, and Jonathan and Einstein hope to bury Mr. Spenalzo in the cellar. Conversely, characters without secrets, such as Mortimer and Elaine, never visit the cellar. The staging of the cellar reinforces this symbol. While the characters regularly reference the cellar and visit it offstage, the audience never actually sees it. This allows Kesselring to use the stage as a means of visually demonstrating the secret to the audience.

The cellar also functions as a more direct representation of the acts related to the Brewster insanity. The aunts hold funerals in the cellar for their victims, and Jonathan wants to use the cellar to bury his own victim and to have his facial operation. Teddy goes back and forth to and from the cellar–however, he is unaware of the reasoning behind his visits and believes he is digging locks for the Panama Canal.