I accidentally left a pocket knife in my carry on as well, and made it through the first leg. On the second leg, I had to go through security again and they sp

I accidentally left a pocket knife in my carry on as well, and made it through the first leg. On the second leg, I had to go through security again and they spotted it. I explained that it made it through the first security check, so it must be safe. They allowed me to keep it. I wonder if that would have worked with a gun...