On page 901 the text reas, "The wedding photo was available for inspection, of course, and confirmed Mrs. Tavis as huge-headed and wildly short." Mario too is described as having a huge head and being the shortest member of a tall family. Also we read the part about "the first birth of the second Incandenza son." Maybe, when Mario's birth is described as a "surrprise birth" it also refers to the fact that Mario is CT's biological son. Remember too that CT avoids Mario at all costs.