As a summer lifeguard when I was younger, I agree with the premise - drowning doesn't look it. Each time I encountered it the key was someone simply staring at me - they don't raise their hands or call for help. It even happened once in my own home swimming pool when a pre-teen got in over his head. His parents definitely didn't notice. Except the very first time when I went over to see what the problem was I now extend a cleaning net to them - they grab on very fast and tightly.