How can they do anything with their hands (partially) in their mouth?
if interested, I can give you the long version.
Short: It is possible chewing your nails off while writing. How? Don't know, maybe one of my kids while finally explain to me. Why? Often it is a reaction to something bothering you (boredom is often the first symptom to be spottet, in most cases there is something lying beneath).
For the horrible story: It has been in the local Hassian Media (as it happened only recently in Offenbach). On the other hand, bad stuff happens always somewhere and at most times even something worse than you really are able to imagine is happening at the same time.