Kristen Bell uses sign language to communicate with her daughter.

The 'Frozen' star, who is expecting her second child with husband Dax Shepard, thinks their 17-month-old little girl, Lincoln, is ''the smartest baby ever'' because she is already talking ''a bit'' and knows ''40-50 signs.''

She said: ''She signs a lot, which is nice. There's a lot of research to suggest that they will be happier if they can communicate before their verbal scores are developed.

''There's a time when they can understand everything you're saying but their verbal scores don't exist.''

She added: ''I can talk to her and she'll sign in three, four word sentences which is really amazing. She'll come in the kitchen and be like [signing] 'More crackers please!' And I'm like, 'Yes, okay!' ''

She added: ''She's MENSA, without a question!? She's the smartest baby ever!''

But the 34-year-old actress admits Lincoln is also already very opinionated.

She told UsMagazine.com: ''It's the tantrum stage.''

Kristen's second pregnancy is going smoothly and she is grateful her hormones aren't out of control.

She said: ''Same as the first one! Really easy, thank God. I've had a lot of friends who have had rough pregnancies and I'm really, really thankful.

''People are affected differently by hormones, we're all different.''