How does Sid show his affection toward Tom?

Sid is Tom's brother. He is the good child who is a foil to Tom's ever-energetic mischief-making. Aunt Polly can rely on Sid to behave, go to school, and not make trouble in church. Tom often resents Sid and feels he needs to get even with him for ratting him out or earning Aunt Polly's favor.
There are two occasions when Sid shows his affection for Tom. The first comes when Tom, who hates school, wakes up on a Monday morning and decides to pretend he is sick. He moans and groans to the point that Sid is taken in. Sid is alarmed that Tom might die:

“Tom, why didn’t you wake me sooner? Oh, Tom, don’t! It makes my flesh crawl to hear you. Tom, what is the matter? . . . Oh, Tom, you ain’t dying, are you? Don’t, Tom—oh, don’t. Maybe—”

Sid's concern shows that he genuinely cares about his brother.
On a second occasion, when the town thinks Tom may be dead, Sid, though he doesn't stay much, does "snuffle" with grief at the idea of having lost his brother.