In his article on asymmetrical spinnakers, Brian Hancock recommends using a cow hitch to attach the sheets to a spinnaker clew. What's a cow hitch?
Eric Watters responds:
A cow hitch (also called a lark's foot or lark's head) is a knot where the midpoint of a continuous sheet is led through the clew ring of the sail and then the bitter ends of the line are pulled through the loop formed by the mid point. To secure the knot, you simply pull the line through the mid point and cinch it down on itself and the clew ring. Another alternative for this application would be a clove hitch, but many sailors feel that the cow hitch is easier to untie after it has been under load for a considerable amount of time.
In the article that you refer to by Brian Hancock (Using the Asymmetrical Spinnaker), the author didn't mention it, but some sailors choose to add a pennant to the sheets on their asymmetrical spinnakers. The pennant can be made of line or webbing, but essentially it's used to attach the sheets to the clew ring while making it easier for the whole assembly to pass over the headstay or headsail when jibing. Often, these pennants have an eye splice in both ends so that they can be attached to both the sheets and the clew ring by way of a cow hitch.
Here's hoping that gives you a better idea of the cow hitch.