Dangerous for sheep

The vivid yellow spires of bog asphodel turn fiery orange in autumn when its seeds ripen. It was once used as a substitute for saffron and as a dye stuff in the north of Scotland. But the plant had a sinister reputation among farmers. Its specific name Narthecium ossifragum  (bone breaker)  reflects the belief that it weakened grazing sheep, causing them to fracture their legs. What wasn't understood was that this plant flourishes in marshy moorland districts where sheep suffered from insufficient calcium in their diet. The connection between the two was entirely co-incidental.
But that doesn't let bog asphodel off the shepherd's crook. It harms sheep in another way. The presence of toxic saponins in the plant interfere with the ability of grazing animals (cows and horses too) to neutralise the effect of chlorophyll. As a result they become photosensitive and suffer severe sunburn on exposed parts of the body, especially the ears, eyelids and any other areas not protected by wool. The condition, called 'elf fire' in Norway, can prove fatal. Now that natural habitats are being preserved and  bog asphodel encouraged  to flourish farmers and environmentalists find themselves at loggerheads. 
  
A fuller explanation of this can be found here.