I’ve had several dogs that seem to be very cautious and even scared around men. I have a nephew that several dogs didn’t want him around. No matter how big or small these dogs even his own would bite him. So I figured that they sense when someone could hurt them. Meaning clumsy or something they smell in the fluids that comes from the mans body, they smell it and that makes them very cautious of him. I say that b/c no matter what dog it was or breed they all had one thing in common they did not want him around. I had one that would hear him drive up and go crazy. So I drew a conclusion that just like a child can sense bad in people so can a dog. And this one particular dog even hated every man that came from that particular family. I figured that the DNA in them smelled so much alike that she identified them all as the same. Strange but true.