This is something you may not have given much thought to, but leeches have wonderful saliva. "Within the leech saliva there is a substance in there called hirudin," Jim Tomsche said. "And there's other things in their saliva as well ... which allows blood flow to expand or vessels to open up their blood supply and also has an anesthetic effect." If that news doesn't make your blood flow, it might some day when you need it the most.