Ivan does not say anything because he cannot speak.
After Rainsford comes to Zaroff's door, Ivan answers with a gun pointed at Rainsford. Rainsford tries to talk to Ivan, but he does not respond. When Zaroff comes to meet them he explains that even though Ivan is incredibly strong, he is "deaf and dumb" which means he is unable to hear or speak.
A short statement or paragraph that tells what something is about
