The arm of the Star Zombie was severed, so of course he wanted to see how it got severed? Where was it severed? Can he retrieve it?
The event happened so suddenly, the Star Zombie just felt something grabbing his arm, subconsciously pulled back, couldn't move it, then the pressure eased, and very soon, it was severed.
Why didn't he use his thoughts to investigate? Because it happened too quickly, he didn't react at all. His arm was in the depths of the God Star, where thoughts couldn't see anything, so he remained dazed, or to put it nicely, entered a state of meditation.
It took him a while to realize his arm was severed because he would never have thought that such a danger could occur in the depths of the God Star.
Up to now, he still wasn't sure if it was an accident, just like having a mouse bite off his finger in a burning steel furnace. No one would believe there's a mouse in the steel furnace.
