In the book, hm, let's see... The Iris probe goes kaput because of the protein cubes I believe. The harmless shimmy, caused by a minor fuel mixture imbalance, rattled the payload. Iris, mounted firmly within the aeroshell, held firm. The protein cubes inside Iris did not. At the microscopic level, the protein cubes were solid food particles suspended in thick vegetable oil. The food particles compressed to less than half their original size , but hte oil was barely affected. This changed the volume ration of solid-liquid dramaticly, this process transfomed the protein cubes from a steady solid to a flowing sludge. Stored in a compartment with no leftover space, the now-compressed sludge had room to slosh. It caused an imbalanced load, forcing the sludge towards tthe edge of the compartment.