Complex sentence: The container used for such leftovers is commonly called a "doggy bag" or "doggie bag"; the name comes from the euphemistic pretense that the food will be given to the diner's pet, rather than eaten by a person.
Split into simpler sentences: The container used for such leftovers is commonly called a "doggy bag" or "doggie bag". It is speculated that this derives from the euphemistic pretense that the food will be given to the diner's pet, rather than eaten by a person.