Germany's new biometric passports are intended to be used with facial-recognition computer scanners, which apparently work best when the pictured face is not exhibiting a dramatic expression. "A broad smile, however nice it may be, is therefore unacceptable." German applicants are instructed to pose only with "the most neutral facial expression possible."
I imagine this will give a lot of security experts a pretty neutral facial expression too. But I guess it will be easy to pick out the terrorists from now on. They will be all the people in the airport who are smiling, in a dastardly bid to defeat the security scanners.