Nuts.  The madibular bone.  Chewing.   Compression.   The work of chewing
something that requires a lot of chewing as nuts do, releases dopamine in
one's brain because of the repeated compressions.  It can be hypothesized
that those who like nuts find the doapmine useful or pleasureable.  I
dislike nuts. I'm more of a serotonin-type person.

Siobhan