Theists want you to believe in miracles. Miracles are the manifestations of God's will on Earth, yet Theists are always willing to say that you shouldn't rely on physical proof to believe in divine power. It is a common human phenomenon called I want my cake and eat it too. I'm going to talk about miraculous healing first and then go onto bleeding "stuff" like rocks, statues, etc.
Let's define the term miraculous healing. Miraculous healing is often depicted as a person in a wheelchair who feels the power of Jesus and leaps up cured. Strangely enough, miraculous healing does not include things like missing arms, legs, eyes, etc.(check out Why Won't God Heal Amputees). One reason why people get better and assume it's by the power of Little Baby Jesus is the Placebo Effect.
The placebo effect is the measurable, observable, or felt improvement in health or behavior not attributable to a medication or invasive treatment that has been administered...There is a dialogue amongst researchers about how powerful the effect is and how it works, but some belief based healing is going on. It occurs regardless of what the object of belief is (doctor, medicine, or god(s)).
By extension, "fake" surgery and "fake" therapies are considered placebos. (from The Skeptic's Dictionary)
Another reason for seemingly miraculous cures as well as statues/rocks that bleed blood is that they are shams. Fakes. Hoaxes. Why would someone deceive legions of followers intentionally? I saw Benny Hinn, the miracle wonder healer, on TV a few years ago. He was doing his act in front of a stadium of people. In the midst of some on stage healing he whisked off his jacket and waved it over the crowd. Waves of people fell (literally) under the power of Benny's holy coat and it's wondrous blessings.
I was just on his website (click here to see it) and Mr. Hinn is selling A LOT of stuff! There seems to be quite a bit of money in the faith based healing. If there is nothing else that we have learned from the Mortgage Crisis and the Oil Geyser in the Gulf is that people do immoral acts to acquire large sums of cash. That's what I suspect from Benny Hinn.
There are those God people who want other people to believe soooo badly that they create Pious Frauds.
A pious fraud is someone whose fraud is motivated by misguided religious zeal (click here for The Skeptic's Dictionary article).What's a little white lie if it brings people closer to Christ? Fake blood is not hard to make. I made it for my last short film and the ingredients are dark corn syrup and red food dye. I found how to make a statue that cries blood on Religious Tolerance.org
In his book "The Unexplained," Doctor Karl P.N. Shuker, mentions a paper by Dr. Luigi Garlaschelli from Pavia University published in Chemistry in Britain. It describes how to make a statue weep.I want to add that there will always be stuff we don't understand. Atheists don't deny that. What Atheists don't do is use God as a way to explaining stuff we don't understand yet.
An except from the book is: "What is needed is a hollow statue made of a porous material such as plaster or ceramic. The icon must be glazed or painted with some sort of impermeable coating. If the statue is then filled up with a liquid (surreptitiously, through a tiny hole in the head, for example), the porous material will absorb it, but the glazing will stop it from flowing out. If the glazing, however, is imperceptibly scratched away on or around the eyes, tear-like drops will leak out, as if materialising from thin air. If the cavity behind the eyes is small enough, once all the liquid has dripped out there are virtually no traces left in the icon. When I put it to the test, this trick proved to be very satisfactory, baffling all onlookers."