(Cow Hitch, Lanyard Hitch)
The Lark's Head knot is used to loosely attach a rope to a spar or ring. The knot has two redeeming features, it is easy to tie, and it does not jam. However, it will slip fairly easily along the spar, and may slip undone when tied using man made fibre ropes.
Tip. This is a knot to be avoided when a secure attachment is required. The Round turn and two half hitches, and the Clove hitch are far more secure.