Sentence:  Fortunately the appearance of the rash marks the beginning of a sudden end to the disease, establishes a diagnosis, <WSD>saves you by the bell</WSD>, satisfies the child's parents, and baby has had just one more kind of measles. 
Meaning of the word marked with <WSD> tags:  To rescue or favorably assist (someone) by means of a timely interruption or the sudden termination of difficult circumstances.