How is Huck almost trapped into telling Aunt Sally he isn't who she thinks she is?

Silas Phelps returns home after picking up his nephew at the wharf. Aunt Sally hides Huck, pretends he is not there, then drags him out and surprises Silas. Silas does not recognize Huck until Aunt Sally announces, "It's Tom Sawyer!" Huck nearly faints from joy when he hears his friend's name and realizes Aunt Sally is Tom's aunt.