Some more Vietnam history today. This picture shows some of the technology used at the time for covert operations and intelligence gathering.
The display box holds three transmitter that would be left in areas with a lot of human traffic. Top left is one made to look like a stick. The top right looks convincingly like a stone. The bottom is most clever, made to look like animal or human feces. I guess the idea is there would be less change anyone would pick it up. On second thought it would probably be the one most likely to be cleaned up if left by a camp if the inhabitants wanted to keep the area clean.