Xander will only play with the ONE ball that he decides is "in play"...and will stare at that ball, follow that ball (say, in another dog's mouth), and will only pick up that ball in a pile of balls. The next time, he could chose a different one...but then THAT'S the one that he plays with. Hard to deal with when we were disc doggin'.
Sawyer plays with invisible toys...'nuff said.
Xander sounds a lot like Cy with decoys..and, yes, in certain situations, not the easiest thing to contend with!
Sawyer - I got nothin!