Then I realized he didn't know how.
His front teeth had never met well enough to allow him to bite off anything that truly required the use of his incisors. When they took the impression of his teeth before putting on the braces, about the only teeth that actually touched were his canines--which explained his preference for softer foods.
So I showed him how to put his teeth together and bite.
This is just one more of life's milestones that most people take for granted. Now Sam can eat corn on the cob...