“And they seized him and they threw him into the pit; and the pit was empty, no water was in it.” (Genesis 37:24)
The Gaon of Vilna notes that the word pit is mentioned twice in this verse, but spelled differently. The first time, the Hebrew word “bor” is spelled defectively without the letter ‘vav’, but the second time, it is spelled fully, with a ‘vav’.
The Talmud notes that since we’re told the pit was empty, why bother telling us that it had no water? The sages teach that indeed, it had no water, but it did have snakes and scorpions (Shabbat 22a).
According to Ramban, the brothers didn’t know that the pit had snakes and scorpions in it. The Gaon of Vilna explained that the Torah initially spelled the word for pit defectively, without a ‘vav’, because the brothers assumed the pit was totally empty. But the second time the word for pit appears, it is written fully, with a ‘vav’, to teach us that the pit wasn’t totally empty – it had snakes and spiders in it as our sages taught.