Mistranslation? A look at ṣela'

On the basis of Adam's statement, combined with these data on usage, we would have to conclude that God took one of Adam's sides—likely meaning he cut Adam in half and from one side built the woman.

When we investigate the Hebrew word and the way that it has been handled throughout history, we discover much supporting evidence for this reading. Beginning with the way that the cognate sélu is used in Akkadian (Assyrian and Babylonian), we find that the word has a certain ambiguity. Rarely, it refers to a single rib. Most times it refers to the entire side or to the entire rib cage. This is comparable to our English use when we talk about a “side of beef.”—The Lost World of Adam and Eve, p. 78