The Professor jumped at the explosion as if he had sat down on one of those small calthrops our grandfathers used to sow round in the grass when there were Indians about,iron stars, each ray a rusty thorn an inch and a half long,stick through moccasins into feet,cripple 'em on the spot, and give 'em lockjaw in a day or two.

Calthrops, or spikes contrived to lame the horses, were also scattered in different directions.