O livro não parece indicar qualquer razão pela qual a cobra escolheu dar uma piscadinha para Harry, além de Harry ter apresentado um contraste com a família Dursley, que estava irritando a cobra e acordando:
... Dudley quickly found the largest snake in the place. It could have wrapped its body twice around Uncle Vernon's car and crushed it into a trash can -- but at the moment it didn't look in the mood. In fact, it was fast asleep.
Dudley stood with his nose pressed against the glass, staring at the glistening brown coils.
"Make it move," he whined at his father. Uncle Vernon tapped on the glass, but the snake didn't budge.
"Do it again," Dudley ordered. Uncle Vernon rapped the glass smartly with his knuckles, but the snake just snoozed on.
"This is boring," Dudley moaned. He shuffled away.
Harry moved in front of the tank and looked intently at the snake. He wouldn't have been surprised if it had died of boredom itself -- no company except stupid people drumming their fingers on the glass trying to disturb it all day long. It was worse than having a cupboard as a bedroom, where the only visitor was Aunt Petunia hammering on the door to wake you up; at least he got to visit the rest of the house.
The snake suddenly opened its beady eyes. Slowly, very slowly, it raised its head until its eyes were on a level with Harry's.
Harry stared. Then he looked quickly around to see if anyone was watching. They weren't. He looked back at the snake and winked, too. The snake jerked its head toward Uncle Vernon and Dudley, then raised its eyes to the ceiling. It gave Harry a look that said quite plainly:
"I get that all the time."
A última linha é importante - note que a cobra fez NÃO tentar falar com Harry primeiro - portanto não escolheu dar uma piscadinha para Harry porque sabia que Harry o entenderia devido a sendo um ofidioglota .