It appears that there are two types of Friesian horses, large black equines and pieces of wood with sharp bits of metal sticking out of them.  Does anyone know how the latter got their name?

The common explanation is that the cheval-de-frise (literally Frisian horse) was so named because it was developed for use against cavalry by the Frisians who lacked cavalry of their own. (See the various entries listed in Onelook.) Cf. caltrop, dragon’s teeth, Czech hedgehog (rozsocháč), and tank trap.