You got that wrong. The rule is "vowel on one side implies even number on the other side". The only cards that don't follow this rule are the ones that have a

You got that wrong. The rule is "vowel on one side implies even number on the other side". The only cards that don't follow this rule are the ones that have a vowel and an odd number. A card with an 8 will never disprove the rule regardless of the letter on the other side, that's why you don't need to turn it.