If you have ever seen a child rapidly flapping their hands or rocking back and forth, you may have wondered what it means.

Most people picture autism as a behavioral condition. Rocking. Repetitive routines. Meltdowns in the grocery store. Those things can be part of the picture, but they tend to show up later. What ...

One readily noticeable pathognomonic trait of autism is hand-flapping—a stereotyped motor movement that can look a bit like an attempt to accelerating the drying of nail polish. Not all with autism do ...