“There is a relic of dry blood which, as the Cardinal Archbishop moves the reliquary, liqufies and visibly flows again.”
Yeesh... if it liquefied on its own in a controlled, pressure, humidity, and temperature invariant environment, while motionless, I might be impressed.
As it is, the bishop is imparting a temperature difference by contact with a warm human body (and friction), and applying a shear force by moving the dried fluid. Both of those actions could cause viscous, dried fluids to re-liquify, with no miracle required.
And of course you can cite secular experts or sources that will confirm your position.
“Both of those actions could cause viscous, dried fluids to re-liquify, with no miracle required.”
Do it. Get some human blood, dry it out, then re-liquefy it the same way.