At around the 18 minute mark of the Extended Edition of The Return of the King, after a slain Saruman has fallen from Orthanc, the Palantir is shown slipping out of Saruman's robes into the flooded ground, before it's picked up by Pippin. However at this moment the Palantir doesn't have any effect on Pippin despite him holding onto it for at least 10 seconds. By contrast, just a few scenes later, it makes him writhe in pain on the floor while holding it, and later on in the film it makes Aragorn faint when he tries to do the same.

Is there anything from the movies or the books to suggest why this is?