A man attends his doctor's surgery to find out the results of his recent serum B12 test which was 141ng/l (140-910ng/l) so the doctor said "That's fine".
"But what about all my symptoms - numbness and tingling in the hands and feet, difficulty walking, muscle weakness, irritability, memory loss etc. etc.etc?"
The doctor smiled and said "I can't treat you as you are in range. You need to increase the amount of animal products in your diet. I have just the thing here"
He reached down and produced a long strip of leather from a drawer in his desk.
"All you have to do, whenever you "feel the need of a boost" is to chew on this leather thong and then come back in three months and we'll test you again".
The man left the surgery bewildered but thought the doctor must know what he's doing and so started chewing.
Three months later the man staggered back into the doctor's surgery and was asked "And how are you today?"
The man slumped into a chair and said:
"The thong is ended but the malady lingers on"