There is a knot in the aran yarn!  Worse there is another knot about two feet further on.  This apparently occasionally happens, I gather it is if snaps during the spinning process or needs a new bit adding on.  When knitting the best thing to do is to cut the yarn before the knot at a row end (even if this means taking the row back to the beginning) and then treat it as if it is a new ball.  Some people,  Aunty Biscuit included, pull out a length of yarn before starting a row which then saves having to take it back if one appears.  This I believe is what happened on this occasion.  What a relief!  I  also have to report that the other foot has now been chewed off my duck toy.