What is the criterion for the transfer of impurity, and is it a condition to see its trace on the garment for its transfer to be ruled, or is it sufficient for a wet impure substance to be touched, even if its trace does not appear?

What we have repeatedly affirmed before is sufficient in clarifying the rule for the transfer of impurity from one body to another: if it is dry, it does not transfer to another dry object that it touches. However, if it is wet, or if a wet or damp object touches it, then it transfers. When there is doubt about its transfer, the original principle is that it has not transferred. So, beware of obsessions and do not rule that impurity has transferred until you achieve absolute certainty of its transfer.