For those still trying to get the 5th giggle to trigger on the doll, try playing through the VHS tape until you've seen the ghost a total of two times during one playthrough of the demo.
I played through the VHS tape after the 1st murder site, unlocked the drawer with the lockpick, opened the pot on the kitchen table, and happened to see the ghost.
I played through it again after the 4th murder site, left the lockpick alone, and didn't see the ghost.
I tried various actions (unlocking the back door, etc.) to see if it would trigger the giggle on the doll, but got nothing.
I played through it a third time, picked up the lockpick, saw the ghost again, went back to the doll, and the giggle triggered.
Two dolls... two ghosts sightings? Just a theory. The common denominator seems to be multiple runs of the VHS tape.