People Walking in Front of You That Suddenly Stop

So I’m walking down the sidewalk with two people walking in front of me and conversing with each other. All of a sudden, one of them says something surprising and they stop dead in their tracks with surprising synchronization, snapping me out of whatever I am thinking about and requiring me to stop as well and walk around them before I can continue on my way. Please, if you must stop while walking, veer off to the side beforehand.