I don't know if Norman Guthkelch and John Caffey had kids, but Caffey wrote in his 1972 paper: > Rhythmic whiplash habits of the infant himself during the firs

I don't know if Norman Guthkelch and John Caffey had kids, but Caffey wrote in his 1972 paper: > Rhythmic whiplash habits of the infant himself during the first months of life, such as head-rolling, body-rocking, and head-banging may be traumatically pathogenic to his brain and its veins. More generally, Caffey considered many types of mild shaking to be potentially dangerous, including "toys and recreational contraptions", "playful practices" etc. The notion that shaking had to be "abusive" to be pathogenic came in the 10 years afterwards.