Sentence:  “We are very grateful to you for coming, sir,” said Alleyn. / “Not at all, not at all,” <WSD>grabbled</WSD> Mr. Rattisbon. “Shocking affair. Dreadful.” 
Meaning of the word marked with <WSD> tags:  To utter inarticulate sounds, often quickly and loudly; to say (something) quickly, idly or foolishly.