I have twin boys, now 18. When they were about 15 I bought them combination locks to use on their school lockers as they kept losing the key versions. I went in the front part of the house with one son who set his combo while his father went up the back of the house with the other son who set his. Neither of the boys knew what we were doing. They had to choose any 5 numbers. They chose the exact same numbers in the exact same order except the last number was different by one (I can't remember the number now but it was something like 11592 and 11593. Creepy!