I have always been concerned about this issue when it came to this area. My husband and I practice a lot, but I am very afraid of something that may prevent me from saying that it hurts or is scary, and he will not understand it and stop. Guys from https://www.bdsmchat.co advised me, as well as a signal, to make a few taps on the nearest surface in case my husband could not hear me. But another question is, what if I'm bound and can't knock on anything? All this is somehow difficult, and so far, I do not understand how to do it correctly and safely