craftgrrl | altered book question!

helloooo, i'm new :)

i saw someone's finished altered book posted on here not too long ago (at least i believe it was in this community..? or maybe it was in the memories, i'm not sure which.. anyway!) and they printed out butterflies on the actual pages of the book. i've thought of doing that before but i have the stupidest question now and i can't find an actual technique anywhere. i'm sure it's the easiest thing but i just can't figure out how to slyly reattach the page to the book! haha, i'm really sorry for the probably really obvious answer, but i honestly am having the hugest brainfart right now. i've looked through the memories and didn't find much about this, specifically -- i just don't want a huge gob of glue somewhere in the middle of book, you know? i don't want it to be obvious that i tore a page out and reattached it. so what's your secret?
again, apologies for the dumb question... any help at all would be much appreciated. thanks so much :)