A funnel can be just about anything. The classic funnel is a wooden fence line across a field that connects 2 tracts of woods. If a deer wants to get from one set of woods to another without crossing an open field they are going to use the wooded fence line. That about the most obvious funnel there is but a funnel could also be something as obscure as a break in a fence line. True deer can leap 7 or 8 feet pretty easy but would you do hurdles if you didn't have to. A break in a fence line is an easy spot to cross and deer will use it. Just about anything that channels deer paths into a smaller area can be considered a funnel.