Right now I tear open the bag but I am sure I could figure out a way to be able to open the bag from the top. I do feel that tearing it open shows that the top is sealed and otherwise, the only way to get that coin out is by tearing open the bag.
Yes!! Any coin can be used, can be signed, there is only one coin used! In fact, you don't have to use a coin. After we did this video, I did the effect to his girlfriend and used her ring!
Keep your creative juices flowing, you actually have something here. Just don't expect to create an effect in two days. You can, with the right presentation, find a way to tell a story as to why you are penetrating zip-loc bag, and why you use the coin, or the ring, or any other small object for that manner. You will find a way, if not, I have one for you.
But, if you want to take friendly advice, DO NOT tear the bottom of the zip-loc bag, it is a dead give away to the method. Why would you tear the bottom, when you can just open the top? If you want to have them convinced that the top is sealed, let them seal the top.
Let me give you a little push. Why would you tear the bottom of the bag, if you can open up the top? Unless... (you finish this sentence).
