Have you ever wondered how many words you know? Or the record number of languages on person has mastered?  A LITTLE BOOK OF LANGUAGE (Yale Univ., $17), by linguist and author David Crystal, is an excellent introduction to linguistics.  Crystal’s discussion is clear and comprehensive, presenting each discrete concept in a concise chapter.  He begins in the womb with a baby’s first exposure to the rhythms of its native tongue, progresses to language acquisition, and by the end has covered sociolinguistics, etymology and grammar, and has explained the capricious spelling rules of the English language.  Crystal even brings linguistics into the 21st century with discussions on Internet etiquette, texting language, and slang.  A Little Book of Language offers a more complete understanding of one of the quintessentially human characteristics. (The answers, by the way, are about 40,000 and 58.)