I know that tail-chasing can mean impacted anal glands, so I checked them out and I think she is ok in that department.  Are there any other possible medical reasons for this or is it just a cure for boredom? (AS IF she doesn't have tons of toys and bones and treats!!   Oh yeah, Ruby is mixed with Shih Tzu and has a long tail).  It is supercute to watch...just curious, thanks...