> In the family of one of those with whom I experimented there were five Jumpers, the father, two sons, and two grandchildren of the respective ages of four and seven years…
Sounds like religion
"Some, if not all, of the Jumpers, are ticklish—exceedingly so—and are easily irritated by touching them in sensitive parts of the body. It would appear that in the evenings, in the woods, after the day's toil, in lieu of most other sources of amusement, the lumbermen have teased each other, by tickling, and playing, and startling timid ones, until there has developed this jumping"