My cat gets cuddly when I read aloud, why?

My cat is not usually cuddly. She lays around the house, and maybe once a day stops by for a quick pet and walks away. She sometimes lays near people, and sometimes not - but doesn't usually seek out attention. I read aloud to my son at night time. Recently, she began joining us every night. While I am reading, she is very snuggly, purring at me and rubbing on us. As soon as I stop reading, she discontinues the snuggling. It is like she is a completely different cat. Any idea why she is doing this?