Daisy, my sheltie, doesnt ever pick up on anything like that. My moms sheltie though, molly..i sometimes call her Nurse molly...anytime anyone comes into the house and has had any kind of injury she goes right to work licking the spot and she wont stop. my fiance went there, he had a bad infection from a ingrown toe nail and i was sure id have to take him to the doctors, he had sandles on and she sat there licking his toe for like an hr, the next morning, his toe was completely healed, u would of never known there had been anything wrong with it.i also had an relative come in from out of state, he had pants on she sat there and licked this one spot on his pant leg till it was soaking wet for hrs, he looked at my parents and said " wow, i dunno how she can sense that, but i had bad infection in my leg 2 yrs ago, i had to have surgery in that exact spot, and its completely healed and you cant tell by looking at it that i had surgery, but somehow she knows".