I looked in a mirror when trying to create a smile. I discovered that when I smile, it reaches the bottom of my eyes, making a crinkle, unless I deliberately forced the smile. Ergo, a smile that doesn't affect the eyes looks like a forced smile. The face in the second pic above, Ron looks like the girl is forcing a smile in an iuncomfortable situation. Like if her 400 lb best friend aske her if the jeans she was wearing made her look fat. (j/k) Seriously, a "silly" smile is often more of a grin, with a lot more eye crinkle. In my own opinion, of course. And one must also consider brow position, and so on. TalmidBen has some excellent advice just above.

Remember, kids! Napalm is Nature's Toothpaste!