My child is sensitive to sound but insensitive to pain. Isn't that contradictory?

How senses are experienced normally differs by type of sense—sound, touch, pain, movement, and so on—and it's common for the same child to have both over-sensitivity and under-sensitivity. Even if it looks contradictory, organizing it as that child's "sensory profile" makes it easier to plan how to respond. An assessment by an occupational therapist can help.