Bernard, an elderly Jew, is bumped by a car while crossing the street.  He is seemingly unhurt, but Sarah, his wife, persuades him to go to the doctor, just in case.
Bernard returns home, and Sarah says –

"Nu, vos zogt der doktor?"  ["So?  What did the doctor say?"]

"Der doktor zogt az ich hob a flucky."  ["The doctor says I have a flucky."]

"Oy, gevalt!  A flucky!  Terrible!  What do you do for a flucky?"

"I don't know -- he didn't say, and I forgot to ask."

Well, by this time Sarah is in a state of high anxiety.  She tells her neighbours "My Bernard was hit by a car, and now he has a flucky!  I don't know what to do!"

Neighbour #1 says, "In the old country, when someone had a flucky, we always applied cold.  Cold is the best thing for a flucky."

Neighbour #2 says, "What are you talking about?  Cold is absolutely the worst thing you could do for a flucky! We always applied heat, that's the only thing to do for a flucky."

Cold, heat!  Oy!  Now thoroughly agitated, Sarah decides to call the doctor herself.  "Doctor, please tell me, what's wrong with my husband?"
"I told him... nothing's wrong.  He got off lucky."