The Gemoro brings a discussion between Ben Bag Bag and Ben Besira regarding possible Simpon, and says that Ben Bag Bag dismisses Simpon as he could not find a possible Simpon. The list of reasons seems quite good (e.g. the master would have seen an visible Simpon, and would not care about a non-visible Simpon etc.)
What Simpon is Ben Besira worried about?
Kol Tuv,
Mark Bergman, Manchester UK
A non-visible Simpon is also problematic, as is evident from the Gemara in Kesuvos (58b, see Rashba there as well). It is definitely possible that someone could be severely disfigured (i.e. through burns, Lo Aleinu) in a way which would not be apparent from an external glance, and would be reason for the Kidushin to be called a mistaken Kidushin.
All the best,
Yaakov Montrose