"Millicent was surprised at the difference between Seth's body tone and that of other babies.
His was soft, she said. The others all felt like pokers."
from: Jean Liedloff, The Continuum Concept
I have done the experiment. I have held some other babies here and there. First I thought that only trianed professionals would feel a difference, or very sensitive people. I was wrong! The difference is very noticeable.
My dd sometimes feels like liquid. Supersoft, so resistance whatsoever. Even on a not-so-good day with not enough movement and opportunities to explore the world, she stills feels soft. Always.
Other children I have held often felt firmer, and I remember one little girl who literally felt like a brick (I felt that only touching her leg, even before holding her). Her parents don't carry her.