Common names range from the poetic to the descriptive to the eminently practical. A number of common names for Kalmia angustifolia land in the latter part of the spectrum: lambkill, sheepkill, and even calfkill.
In addition to names reflecting its toxicity to livestock, Kalmia angustifolia is perhaps best known as sheep-laurel. The toxicity is due to the presence of grayanotoxin I, also known as andromedotoxin (and discussed in detail in the entry earlier this year on Rhododendron tomentosum subsp. decumbens). The Canadian Biodiversity Information Facility provides details on the effects of sheep-laurel poisoning in human and livestock.
The University of Maine Cooperative Extension Office has additional images of Kalmia angustifolia.