I've gathered a few scenes from youtube to use for my own reference while writing, and figured I'd post it so everyone else can get a short, quick and dirty idea of what your character is seeing/hearing when interacting with Ivar, since both his voice and mannerisms are not entirely normal (and then I added a few just because.)
(SPOILERS through Vikings season 5A)
Ivar's gait (and pained noises) when he walks on his crutch: