Wet Behind the Ears

The image is usually explained as a newborn animal, or a newborn baby, still damp from birth, with the area behind the ears being one of the last spots to properly dry. It's a vivid, plausible picture, but the phrase's actual roots trace back further than that explanation alone: the Oxford English Dictionary points to a German idiom from the 1640s meaning almost exactly the same thing, "still wet behind the ears," which may be the true origin point English later borrowed and adapted. The phrase first shows up in English in a negative form, "not yet dry behind the ears," and became an established American phrase by around 1902.