Okay, so it's no sweat to write a letter, but delivering it when you are a teeny tiny little borrower? Pretty difficult.
Arrietty had been trying to hide the letter she wrote to her uncle under the mat for the boy to pick up for days with no luck, until Homily convinces Pod to go borrowing again for some blotting paper. Arrietty tags along, slipping the letter under the mat without her father noticing.
When Arrietty and her pop bring the blotting paper home, Homily freaks out, saying that she heard Mrs. Driver say that the boy has been up and about again, looking desperately under mats in the hall for something.
We think we know what he was looking for.
Arrietty does too, and is heartbroken, because she thinks the boy will never think to check under the mats again, since he looked for so many days in a row and came up empty.
Here comes the part where Arrietty lies to her parents, which Shmoop most definitely does not recommend.
Every evening she stands on a stool in her kitchen, pretending to practice getting "a feeling." But really, she's eavesdropping on Mrs. Driver's conversations with Crampfurl.
This particular evening, she overhears them drinking Great-Aunt Sophy's favorite wine, and talking about how the boy must have a ferret, because he keeps running around in the fields poking his head in badger holes, looking for something all day.
And he keeps calling some name that sounds like "uncle."
Could it be he got the letter and is looking in the badger holes to deliver it to Arrietty's Uncle Hendreary?