Harry was pointing the wand directly at Dudley's heart. Harry could feel fourteen years’ hatred of Dudley pounding in his veins—what wouldn't he give to strike now, to jinx Dudley so thoroughly he'd have to crawl home like an insect, struck dumb, sprouting feelers—
‘Don't ever talk about that again,’ Harry snarled. ‘D'you understand me?’
Harry Potter and the Order of the Phoenix
I think "what wouldn't he give to strike now" implies Harry really wanted to strike, right? However, I don't understand the grammar of "struck dumb, spouting feelers", and I'm not sure how to link it to the sentence. Is it modifying "an insect" here?