In Chapter 6, what significant discoveries does Jem make because of his return?To Kill a Mockingbird by Harper Lee

On a moonlight summer night, Dill, Jem and Scout venture
into the Radley backyard in order for Jem and Dill to look through one of the dark
windows of the Radley house and discover what they can.  However, as Jem climbs one of
the steps, there is a prominent squeak.  Scout, waiting for the boys, now perceives the
shadow of a man with a hat, a shadow that crosses before Jem.  Then, it turns and goes
to the side of the house where it reenters as it has come.  Terrified, Jem leaps from
the porch and he and Dill attempt to flee, but Jem catches his pants on the fence.  He
writhes out of them after hearing the blast of a shotgun over his
head.

Knowing that the neighborhood will come into the
street with this thunderous sound, the children sidle beside Miss Maudie, unobserved at
first.  However, Atticus notices that Jem has no pants.  But, glibly Dill lies, saying
that he won them in strip poker.  Jem, too, lies to mitigate the horror of Dill's aunt
that they were gambling; Atticus tells him to retrieve his pants from Dill.  Of course,
Jem feels he must secretly return to the Radley's for his pants lest Atticus learn of
his lie.  So, he sneaks out and Scout waits for him to return.  He does;
however, instead of his pants awkwardly suspended from the Radley fence, they are neatly
folded over the fence for Jem's return.  Jem discovers them there and realizes, too,
that they have been roughly repaired.  Scout remarks,

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"--somebody knew you were comin' back for
'em."

"like somebody was readin' my
mind..."

Jem shudders at the
thought.  The children are further spooked as they consider that someone knew what Jem
would do.