Caltrops

See also: trapping, mines

Used as early as 300 BCE by the Persians. In modern times caltrops tend to be attributed to ninjas, who if they (specifically ninjas) ever really used them, only did so much later during the Japanese feudal period (12th to 19th century CE).

Some variants have hooks to make removing them more injuring and painful than the initial puncture. Other more modern variants have hollow spikes to make them able to puncture vehicle tires and counter any auto-sealing they may have.

The slowing effect is threefold: firstly actually stepping on the device, causing pain and bleeding as well as slowing down anyone who stepped on one for a significant amount of time. Secondly victims will likely slow down in general to observe the ground more to avoid stepping on them again. And thirdly, if significant number of personnel need to pass (especially if animals are involved), collecting/removing the caltrops is required which may add yet more slowness to bypassing them.

The injury itself is mild in most cases, but falling down on caltrops can be fatal. For example, if one of the spikes penetrates one's skull as a result, or if they manage to sever major arteries.