Medical texts reveal that the Egyptians knew that the beating of the heart (called 'speaking') could be felt at various places in the body. According to the papyri, the movement of the limbs was determined by the heart. It is unlikely that the heart was recognized as the organ that pumps blood through the body. Nevertheless, the Egyptians were aware that the heart was the most important organ. The reason for this is that they thought that the heart was the seat of wisdom, memory and emotions. The Memphite creation myth, for example, tells that Ptah conceived the creation of the world with his heart. Because it was such an important organ, the heart was left in the body at mummification or, if initially removed, put back. Only in earliest times was it sometimes replaced by an imitation heart, as is suggested by one of the Pyramid Texts from the Old Kingdom. The common idea that the heart scarab was meant to replace the removed heart is incorrect. The Egyptians also feared that the heart would be stolen or lost in the underworld; spells from the Book of the Dead were designed to prevent this. Representations of the Divine Tribunal in the Book of the Dead show the heart of the deceased being weighed against a feather representing the goddess Maat or truth. Next to the scales sits the monster Ammut, ready to swallow the heart if the result is negative thus causing the deceased to die 'the second death'. The deceased was given a heart scarab to help him through this critical moment in the judgement, and to prevent the heart from causing a negative outcome.