Stupidity: When Doss buried the wounded soldier, leaving one eye out made no sense. It did nothing to help him. All it did was make it easier for the Japanese to spot him. It would've made sense to leave his nose and/or mouth out, so he could breathe. He did not need to see.
Suggested correction: A person who is unable to see is more likely to panic. When Doss buried the wounded Marine, he asked him to take a deep breath and trust him. By leaving one eye open, it allowed him to see the gravity of the situation as IJA soldiers walked by and maintain eye contact with Doss who hid under a dead Marine. After the suspicious IJA soldier bayoneted the body over Doss, he looked directly at where the wounded man was buried and kept walking. It was a crude method, but it likely saved them both.
Stupidity: When Sook-Hee walks into Hideko's bedroom before the two of them have sex, she slides the door open when going into the room and never closes it behind her. Once the two of them are in bed together and when they have sex, the door is left the way it is and never closed. Considering a sexual relationship between the two would have been completely forbidden, and, if they were caught, would likely ruin the plot to steal the inheritance money, it seems very foolish of them to ignore the open door, especially taking into account there are other people inside the mansion who could walk by at any moment. (00:41:30)