Does swallowing a very small amount of food that was eaten out of forgetfulness and then spit out invalidate a compensatory fast, and must that day be made up or completed?

Eating or drinking intentionally invalidates the fast, but doing so forgetfully does not, according to the majority of scholars. They cite the Prophet's (peace be upon him) saying: "If any of you eats or drinks forgetfully, let him complete his fast, for it was Allah who fed him and gave him drink." So, whoever swallows food forgetfully, his fast is valid. But whoever swallows it intentionally, his fast is not valid, and he must make up another day. If a fasting person breaks his fast while making up a missed day, he is not obliged to refrain from eating for the rest of the day; rather, he only needs to make up another day.