The Jewish litmus test

Mordechai was telling me and neighbor Penina that his busdriver, Sylvester, claims he's Jewish. He sometimes wears a kippa and, on Fridays, says he has to rush home after his route to get ready for Shabbos. (Mordechai imitates his accent cutely. Sylvester is African-American with an accent from...I have no idea where. But there is an accent from somewhere.) Obviously, this is all to play around with the kids. He's really nice like that. Penina asked Mordechai, "Does everyone believe him?" A look of doubt flickered across Mordechai's face before he replied, shaking his head, "Well, I asked him what the first holiday in Jewish is and he said he forgot and would have to learn that again so..." Oh, well. Guess not.