My 4 year old wants to read the same picture story book again and again, how do I vary it ??

I went to a seminar and they say normally kids will only remember a word after we say it 250 times so I guess they don't remember that they read it. My girls also ask to tell them the same bed time story every night. I guess it's good cause after repeating so many times, they can remember the story and will tell me the story back. Or if I twist the story alittle, they will say it's wrong. Think that is how they learn I guess. Practice makes perfect.