“leg on thigh.” This is an idiomatic phrase that occurs only here and has not been found in other ancient literature either, so the exact meaning is unknown. However, the sense has to be one of total slaughter.
“cave.” The word “cave” is not technically correct, but this is a case where the English has no word that exactly reproduces the Hebrew. The Hebrew refers to a cut, crack, or cranny in rock or a rocky place that has overhanging rock over it for shelter. Thus it is more like a cave than a “cleft” or “crack,” which has no overhanging shelter.