What Happens When a Miracle Happens at Mass?

There are a couple of reasons for caution here. Stage magicians use slight of hand techniques to make objects seem to appear and disappear in front of hundreds of people all the time. The moment of the miracle isn't typically witnessed by hundreds of people. This means that we have one initial witness to something strange, and that witness often doesn't claim to have seen the moment of transformation. Consequently, from a sceptical viewpoint, we can't rule out that someone, either the witness or some one else, didn't do something surreptitious to make it look like a miracle that happened.