Here is a candid shot of my son:
And here is posed photograph, taken seconds later:
As you can see, he has mastered the art of saying “cheese” without smiling.
Worse, we accidentally trained him to associated cameras with the saying of “cheese” rather than with smiling, so the face above is what appears in everything from school photos to pictures with Santa Claus.
It is a real problem but not one without a solution, as he demonstrated one afternoon by running into the kitchen like this: