Some snakes (that are egg eaters) have a special bone in the rear of their throat that pierces the eggshell and then the snake does a little squeeze with it's throat muscles and the egg contents spill out into the shakes gullet and goes on down to the stomach. The eggshell is then orally expelled. When a snake like above eats an egg it is not long before the crushed eggshell reappears.
Some shakes have strong digestive juices or acids and these shakes partially or completely dissolve the eggshell. Even if the eggshell is not completely dissolved the shake moving to a different stronghold while it's stomach acids work may well mean that you will not see the expelled eggshells.
Some shakes have strong digestive juices or acids and these shakes partially or completely dissolve the eggshell. Even if the eggshell is not completely dissolved the shake moving to a different stronghold while it's stomach acids work may well mean that you will not see the expelled eggshells.