The following is from a public health aid worker's blog in Senegal, link.
"I was asking an elderly woman about her vision and had a hard time understanding her answers in Wolof. Generally if I ask, “Can you see well up close?” they answer with something complicated, like “Well, I can see to sew sometimes and to read letters from my friend, but not in the sun.” I love simple yes and no answers, but that’s irrelevant. This woman and I were not communicating well so I held up an index card and asked if she could read the writing on it. She squinted and squinted, but said nothing. I asked again. Same response. I turned the card over to see that I had picked up the only index card in the stack that was blank!! Ooops."
Indeed. Reminds of my exam dream with the blank question paper..