I have a new client, who after the first session, said that rolling like a ball and seal left her with actual blisters on her tailbone. Since then, I have had her to just hold the position without rolling. I have heard that some people have an extra vertebrae in their sacrum that makes such positions uncomfortable. I do not know that this is the case, but I suspect it is possible, since she has not had any known injury to the area. Have any of you more experienced instructors run across this particular issue before, and if so, do you have any suggestions? Thanks in advance.