Evaluate the valence intensity of the following sentence, considering the mental state of the author. Present a score between 0 and 1, where 0 denotes extremely negative and 1 denotes extremely positive.
Sentence: The long blade of the yucca had a sharp tip, but the only weapons allowed according to Humpty Dumpty Nursery rules of engagement were smelly thistles or cocklebur stems covered with spiked yellow stickers.