understanding the 3 year old mind

Last night Russ was going to read the girls a book before bedtime. When Lizzie saw the book she jumped up and said, "No Daddy! You can't read that book - it's weird!" The book was "Click Clack Moo." So she ran and got another book by the exact same author called "Giggle Giggle Quack." Any thoughts as to why one was weird and the other wasn't???