The word "拉屎" is formed by combining the character "拉", which functions as a verb meaning "to pull" or colloquially "to discharge", with the character "屎", a noun meaning "feces". This creates a verb-object compound where the action denoted by "拉" directly acts upon the object "屎", resulting in a literal sense of "to pull feces" and an idiomatic meaning of "to defecate".