Good Riddles

Question: I can be seen, I can be not. Thanks to me, you'll fall in love. I mostly am sweet, but once I were sour. You can receive me, you can't just buy me. You only can send me, or simply share me. What Could I be?

Question: Mary and jack are newly weds and want to go on a ski trip... So jack starts planning. He books a flight for them to Colorado. When they get there Mary gets pushed off the cliff. There is a guy in Hawaii named Sam and he was reading the paper. He right away said the husband did it. How does he know? HINTS: they have never met in person, jack did not tell Sam, he was not guessing, and it did not say it in the news paper.

Question: It makes everyone blind. You can't see it and it will always come back for you.

Question: what is ready when you add a letter inside?

Question: Which kind of board can you use to insert letters?