I'm not normally full of praise for him, but fair play to Dessie, he let out a perfectly appropriate AAAaaahhh at the sight of the Townend incident and then got on top of it quickly.
I can't find a convincing explanation for Townend's manoeuvre. Horses were veering right at the previous fence but not so much in the approach to the last. I wondered if his horse had gone lame, but in that case he wouldn't have started pulling on his left rein to belatedly try and keep him on course.