A Knot of Snakes

Things are hotting up at the grass snake pond. Today I was fortunate enough to witness a mating ball of writhing snakes. They were, uum, at it, for about half an hour before I left them to it.
I don't like the "mating ball" description as it seems a bit unimaginative, so I Wikied collective nouns and decided that a "knot of snakes" is a more fitting term.
How many can you spot?