I don't know how sensitive Genome tails are canon-wise (I'm guessing similar to any animal with a tail; if it has nerves then they will certainly react) since the only clue we really got was Zidane getting incredibly pissed off when Laguna pulled his tail. I'm guessing that must've been somewhat painful even with Zidane's tail being used to hard labour when it comes to supporting his weigh and all. Since Kuja shields his tail away it must be extra sensitive. Which means all the more crack/kink potential! 8D

Kuja couldn't handle 5 seconds of it. Or even 2. I bet even with Terra he can easily be controlled by the tail...