Possible Clues:

• How the river's willing to be the death of you
• Arrow application
• The river one is on may be the death of one
• Toxin or venom
• Meat for someone else? Nothing eaten by good boy
• Gutted fish from France contains pesticide, maybe
• Scull-and-crossbones stuff
• Eg, toxin
• About one spoon of this might do for one
• Another man's meat is dangerous stuff