Maybe you see a plant you have to collect in game or a rock wall that looks different. What items have you caught out of the corner of your eye that you realized was just your brain so focused on looking for things in a game that you saw it IRL and made you double take?
After playing too much Ghost Recon, I once caught myself looking for a ditch I could jump into before “the guards” would come out of a farmhouse I was going to. Took me a full minute or two to shake off the feeling.