Till a dart strike through his liver; as a bird hasteth to the snare, and knoweth not that it is for his life.
– Proverbs 7:23
[A]n arrow to the liver is a mortal wound. Life is in the balance. It could be more immediately or ultimately. The way of fornication and adultery is a way that only ends in death. The last image is the bird going for the bait in the snare unknowing the snare means its life. Again the thought conveyed is that the young man doesn’t really comprehend what he is doing, nor the great cost associated with it.