1.43. The king dies and two men both claim to be his
long-lost son. One of the king’s advisors proposes a test to determine the
identity of the true heir. One claimant agrees to the test; the other
refuses. The one who agreed is sent packing; the one who refused is
identified as the rightful heir. (SP, from The Next Book of OMNI
; earlier from How Come?)

1.43 answer: The proposed test was a blood test. Knowing that blood
typing isn’t very accurate, the impostor felt it was worth trying to get
away with it. But the true heir was a hemophiliac and couldn’t give blood
for the test.