Possible Solution

"Your head is obviously the one that's speaking, nitwit," Atticus said with a deadpan. He was the first to recover from the surprise, rolling his eyes at the stupidity of the prince. It seemed like after his beheading, Prince Silas's brain became useless as well.

"I killed you! We all saw it!" Leonora exclaimed, with a shaky voice and even shakier legs. 

She sank to her knees and gestured wildly to Silas's beheaded body lying quietly on the floor, a contrast to his still sentient head. Thankfully, it didn't seem like the body was regrowing another head any time soon. 

"Silas, how are you still speaking?"

"How would I know?" Silas screeched back at Daphne. He then turned — or as best as he could — to Leonora. "You obviously didn't do a very good job at killing me, if I can still speak!"

"That's nonsense!" Leonora spluttered, appalled. "I've killed more people than the number of times you've slept with a woman!"