
Sofia G. answered 04/02/19
Dedicated Tutor with Specialty in Gifted and Talented
Hi! Without knowing the rest of the story (Ron and Harry's relationship at this moment in time, for example), it is difficult to give you a precise answer. It has been a while since I read the Harry Potter series... What I CAN tell you is that "Harry grinned into his pillow" means just that - he turned his face toward his pillow (or against his pillow) and grinned. It's basically telling us (the reader) that he was feeling excited about what he was imagining. Plus, his imagining Cho looking at him (Harry) with a look of "admiration", is also making him feel extra excited. We can see from the text that Harry has these secret desires - winning, being a champion in other's eyes, being admired by someone he likes (maybe even admires too), maybe the hint of a crush... All these secret desires that he may not be ready to share with his friend, Ron, is causing him to grin secretly (here's where the pillow comes in - to hide the grin from Ron). The images in Harry's mind and the feelings they stir up could cause him to be feel a bit embarrassed. This could be why he's glad Ron can't "see" them.
Hope this helps!
Cheers,
Sofia G.