We were entering the US at Montana's Chief Mountain port in a car rented at the Calagary Airport a few hours earlier when we seemed to be receiving many more questions than during one of our usual crossings. One of the two agents abruptly reached into the car and popped the trunk lid - never happened before. As the questions continued on and on I realized that I had not removed my sunglasses. Only moments after I did so the questions stopped and we were waived on our way. I think I learned a lesson that visit.