In ''the wretched beggar cleaned his nails with dry saliva'' the device used is

The device used in the given phrase is an oxymoron. An oxymoron is a figure of speech in which two contradictory terms or ideas are combined to create a rhetorical effect. In this case, "wretched" (which means miserable or pitiful) and "cleaned his nails" (which implies a certain level of hygiene or self-care) are contradictory terms that are used together to create a striking and unexpected image.