Imagine that you have pair of socks. You sent one sock to Alice and the second sock to Bob. When Alice opened her package, she sees the left sock, so she immedi

Imagine that you have pair of socks. You sent one sock to Alice and the second sock to Bob. When Alice opened her package, she sees the left sock, so she immediately knows that Bob received the right sock. This is the FTL communication. Alice can forcefully change her sock from left sock to right sock and back, e.g. by putting sock to the corresponding foots, but Bob will never know that.