Back to the 'Tunnels of Cu Chi', I find this project hard to believe. Thought up by the Limited Warfare Laboratory (LWL) the idea was to carry a box full of bedbugs as they could smell human flesh and would let out a yowl of excitement. This yowl could be measured and it could warn against ambush attacks.
"The project collapsed when it was discovered that the bedbugs couldn't control their excitement. They became so deliriously happy at just being carried about by GIs that they were too busy 'swooning with delight' to warn their patrons of any approaching Communist ambush."