Can you kindle a fire on Yom Tov even when not needed for cooking?
H2: Kindling from an existing flame is permitted even when not needed for food. This is one of the holiday's unique leniencies. But creating new fire (striking/rubbing) is always forbidden.
Question 2
Your house is on fire on Yom Tov. Can you extinguish it to save your belongings?
H4: Extinguishing is forbidden even for property. You must let it burn. Only pikuach nefesh (danger to life) overrides. Money isn't worth violating the holiday.
Question 3
Why does the Rambam say "don't publicize" the permission to whet a knife on wood or stone?
H9: Whetting on wood is technically permitted, but looks similar to prohibited grinding-stone sharpening. The Rambam fears people won't distinguish — so keep this leniency quiet.
Question 4
A utensil became impure the day before Yom Tov. Can you immerse it on Yom Tov?
H17: The freshness/advance-preparation test strikes again. If it became impure before Yom Tov, you should have immersed it then. Only items newly impure ON Yom Tov may be immersed.
Question 5
At the butcher on Yom Tov, how should you request meat?
H21: "A portion" or "half a portion" — not monetary amounts. Settle the account after the holiday. The language of commerce (prices, weights, measures) must disappear on Yom Tov.