The secret message in the film
There's a secret message that you can discover in (***SPOILER ALERT***):
The FIRE, the GRASS, the factory WINDOW, the GRAVESTONE and the RUG. All-together it spells: "Seek me no further or...". This combined with reversing Tristen's backward words in the last act reveal the secret of 'ESREVER': "Seek me no further or... the children will again walk free." This means the Blair witch would loose the spirits of the murdered children to torment the invaders of her domain.