As the body ages, the brain naturally starts to slow down a bit. Things you used to know in a split-second take a bit longer to recall. Learning new information might not be as easy as it once was.
One way to stay sharp is to exercise your brain directly with games, puzzles and even optical illusions. These don't have to be all that hard, just a bit challenging. Of course, to stay challenging you need to tackle new puzzles and games every so often. And wouldn't you know it, there's more than enough optical illusions online than anyone could consume in an entire lifetime.
But some illusions have more of a "WOW" factor than others. Here are the four latest optical illusions to go viral online. Can you figure them all out?