Theory:

     But Sid had snatched his clothes and gone. Tom was suffering in reality, now, his imagination was working well, and so his groans had gathered quite a genuine tone.
 
     Sid flew down-stairs and said:
 
     “Oh, Aunt Polly, come! Tom’s dying!”
    
     “Dying!”
 
     “Yes’m. Don’t wait. Come quick!”
 
     “Rubbish! I don’t believe it!”
 
     But she fled upstairs, nevertheless, with Sid and Mary at her heels. And her face grew white, too, and her lip trembled. When she reached the bedside she said, “You, Tom! Tom, what’s the matter with you?”
 
     “Oh, auntie, I’m---”
 
     “What’s the matter with you? What is the matter with you, child?”
 
     “Oh, auntie, my sore toe’s dying!”
Explanation:
 
Sid went to his aunt gathering his clothes. Tom was so much into it that his pain was feeling like truth. Sid went down and called out on aunt Polly saying Tom is going to die and asked her to come as soon as possible. Though aunt did not believe him, but still she ran upstairs with her lips trembling and face turning pale. Sid and Mary followed her as Mary is Tom's cousin. Aunt asked Tom what had happened. Tom replied his sore toe was dying.
Reference:
State Council of Educational Research and Training (2018). Term-1 English Standard-7. On Monday morning - Adapted from The Adventures of Tom Sawyer by Mark Twain (pp. 18-21). Published by the Tamil Nadu Textbook and Educational Services Corporation.