Pigeons. Uncle Volcano's favourite bird.
In fact, Uncle Volcano didn't like any sort of birds, including fit birds, which Hairy liked very much. Aunt Prudery didn't count as a fit bird as she was old and had a moustache.
Wizards usually receive their post by snails, but Hairy was clever. He realised that you can actually go and fetch your post yourself and be quicker about it. Albus Bumblebee also became rather bored of this method and so switched to pigeons, with which he has an affinity. Soon, hundreds of pigeons were delivering post its to Hairy.
The problem was, Aunt Prudery was so disorganised she needed to stick post its everywhere. She even stuck them to Dumbo's trunk - they were then visible all through the day, especially when he was eating. But when Hairy began to receive post its, the two became mixed up.
When Aunt Prudery picked up a post it (delivered faithfully by a pigeon) and read it, she fainted. Uncle Volcano erupted at the sight, and asked her whatever was the matter?
"Warts! I HATE warts! But not just any warts! HOG warts! Yuck! Why would I remind myself about that? Dumbo, does Mummy have warts?"
After much detailed examination of the subject and the evidence Uncle Volcano finally simmered down and came to the conclusion that Hairy had hog warts.
"Boy, what do you mean by this?" said Uncle Volcano. "You're putting me off my dinner."
"My warts are nothing to the volcano on your head," said Hairy, trying to avoid the admonitory eye of a particularly voluminous pustule.
This earnt him a particularly long punishment in the shoebox, with only his pet laces for company. By the time he'd escaped, the house was full of post its. The pigeons had been unable to deliver them to Hairy - so instead they started pouring out of the refrigerator. Aunt Prudery was having fits - all the neat post its on her fridge were being muddled up! Eventually, the stress became too much for Uncle Volcano. He exploded that they would be leaving ... straight away.