I still can't see for s***, even when magnified but... it looks kind of like a grace note which is a type of hammer on used by SRV. Although I have no idea how one could play an open string grace note. The hammered "5"s in the following pic are grace notes:

Something to look into anyways. It's a reallly cool sounding technique. Unfortunately, this is from TrueFire site so I have no way of linking to it.