Jamieson, Fausset and Brown on 2 Samuel 13:6-8

6-8. Amnon lay down, and made himself sick--The Orientals are great adepts in feigning sickness, whenever they have any object to accomplish.

let Tamar my sister come and make me a couple of cakes--To the king Amnon spoke of Tamar as "his sister," a term artfully designed to hoodwink his father; and the request appeared so natural, the delicate appetite of a sick man requiring to be humored, that the king promised to send her. The cakes seem to have been a kind of fancy bread, in the preparation of which Oriental ladies take great delight. Tamar, flattered by the invitation, lost no time in rendering the required service in the house of her sick brother.