Little Johnny returns from school and says he got an "F" in arithmetic.
"Why?" asks the father.
"The teacher asked 'How much is 2x3?' I said '6.'"
"But that's right!" The father replied.
"Then she asked me 'How much is 3x2?'"
Calcium deficiency causing white spots on nails is the most common myth, followed by zinc deficiency. The truth is that white spots are common and harmless and don't indicate any specific vitamin deficiency at all.