I was wondering what abilities can be stopped with casting a taunt, knock-up, pull etc. I know that when Shen uses his shadow dash while Karthus is channeling his Requiem it will cancel Karthus his Requiem. Now i main Darius and naturally i was wondering if it was possible to taunt(, knock-up, pull etc) Darius while he uses his Noxian Guillotine to cancel the ability. Then i wondered since that might be possible what other abilities that have even the slightest of casting animation could be stopped by taunting, knocking-up, pulling, silencing, etc. Think Nunu ult, Jarvan ult (if you taunt while he is jumping?), Twisted Fate ult, Shen ult, Fiora ult, etc.
Since this part of the question expanded it by quite a bit what would be the criteria of canceling an ability. If an ability animation gets past a certain point in which it cant be stopped, instead of a milisecond earlier when it could be stopped?