Once in a while example sentences

Although the family has difficulty in arranging two meals a day, Sivaraman manages to buy milk once in a while, but only for his son.So once in a while a comet comes close to the Sun; it has a longish tail that is lit brilliantly by the sunlight and then it recedes into darkness not to be seen again for years, or for centuries.Their correspondence never mentioned the Project Light Brigade although once in a while Sir John would hint at its progress in a subtle manner that Duttada would understand.