Apparently, he has one more symptom, his body's making an extra antibody, type B. Combine that with his natural type A, and presto change-o, he magically pulls blood type AB out of his hat.
Because your body only makes those antibodies when you actually have that type of blood.
[SEP] Because your body only makes those antibodies when you actually have that type of blood. [SEP] Apparently, he has one more symptom, his body's making an extra antibody, type B. Combine that with his natural type A, and presto change-o, he magically pulls blood type AB out of his hat.