What u/NightlyWry and u/Trick-Two497 said. This. Very wholesome. This is a really good way of letting him know this means a lot. You can both crack a couple of light-touch gags about reading it cover to cover - or not... And if you don't have a favourite insect, ask him to find the bit in the book that describes his. Or ask him to share his favourite bit in the book. There are ways of sharing your appreciation that don't involve pushing your way through a book you aren't going to enjoy - and he'd never want that.