"and I guess the laws of Nature are not going to be suspended for the British aristocracy...."See in text(Chapter I.)
Wilde wrote "The Canterville Ghost" as a twist on the traditional ghost story, as a satire of American materialism, and as a way to parody English culture as well. This section satires both American and English cultures by highlighting Mr. Otis's reliance on practicality and common sense and the English aristocracy's self-inflated perception of itself.
Wilde again satirizes American faith in materialism and ingenuity in this passage. Rather than believing that his trusted detergent is either defective or ineffective, Washington concludes that supernatural activity must account for the reoccurrence of the blood stain.
The Society For Psychical Research was founded in the United Kingdom in 1882, five years before "The Canterville Ghost" was published. Their stated purpose is to understand and comprehend psychic or paranormal activities that fall outside the range of scientific behavior. Mrs. Otis's willingness to join the group and inability to distinguish between science and pseudo-science parodies the Victorian era's faith in scientific progress.
"to stand between them in the form of a green, icy-cold corpse,..."See in text(Chapter III.)
Similar to the "of course" explanation above, this phrase suggests that the ghost has no other options besides looking like a corpse because of the role its playing. Wilde appears to be using all the possible clichés of traditional ghost stories for Sir Simon's plans, and the inclusion of all these clichés satirizes the tradition.
"The first thing to be done was, of course,..."See in text(Chapter III.)
The phrase "of course" gives the impression that the narrator is sharing important, confidential information with the readers and confirming the ghost's actions as logical and appropriate. However, since the phrase is set between two commas, readers should note that this indicates Wilde's intention to signify the opposite meaning: the ghost's actions should be seen as absurd and playing into the classic tropes of ghost stories.
"which is the reward of all good little American girls,..."See in text(Chapter VII.)
Wilde is likely pointing out the irony in how even though the US doesn't have royalty or an aristocracy, the dream of becoming royal, a prince or princess, still persists in the popular imagination of many young people. The ending to The Canterville Ghost represents this as well, with the young heroine being rewarded with jewels, a handsome prince, and a happily ever-after.
"can only account for it by the fact that Virginia was born in one of your London suburbs..."See in text(Chapter VII.)
Mr. Otis is so puzzled by Virginia's ability to sympathize with the culture of England and Europe that he reasons that she must be this way due to the circumstances of her birth. His reasoning here further highlights Wilde's satirical portrayal of Americans and their desire to find a practical rational for everything.