If it ate grapes yesterday , it will eat grapes today with probability 1\/10 , cheese with probability 4\/10 and lettuce with probability 5\/10 . Finally , if it ate lettuce yesterday , it wo n't eat it again today , but will eat grapes with probability 4\/10 or cheese with probability 6\/10 . Another example is the dietary habits of a creature who eats only grapes , cheese or lettuce , and whose dietary habits conform to the following ( artificial ) rules : it eats exactly once a day ; if it ate cheese yesterday , it will not today , and it will eat lettuce or grapes with equal probability ; if it ate grapes yesterday , it will eat grapes today with probability 1\/10 , cheese with probability 4\/10 and lettuce with probability 5\/10 ; finally , if it ate lettuce yesterday , it wo n't eat lettuce again today but will eat grapes with probability 4\/10 or cheese with probability 6\/10 .