Refresh a few times, it seems to present examples randomly, and some are much more close up than pixel-wide.
Regardless, consider the job of the lifeguard: They don't have the benefit of clear close-up sight of all swimmers. If you can't spot the drowner when you know there will be one, imagine how much more difficult it is for a lifeguard who doesn't know when a crisis will occur.
Unless you're willing to go to lifeguard school, learn to train yourself on the hard-to-spot examples without explanatory details: you'll be a lot more likely to gain a potentially life-saving skill.