פירוש על עבודה זרה 60:4

When a fig is picked a little hole is left where it was attached to the tree. R. Hiyya b. Ashi says that one need not suspect that the snake drank from there. But the Talmud’s comment implies that the snake may indeed have drank from there if left uncovered. Nevertheless, one may eat the fig because God protects people.

The point of knowing that the venom sneaks to the bottom is that nine people can safely drink from a barrel of liquid or eat from a melon and live, and the tenth can die.