A Jill sandwich is a zombie delicacy, prepared by crushing S.T.A.R.S. member Jill Valentine (of Resident Evil fame) in a room with a slowly-descending ceiling. When Jill is reduced to a nice, squishy pulp, zombies spread the resulting pulp between two slices of bread and enjoy a nice snack. Alternatively, if zombies are out of bread, they can proceed to lick the Jill pulp off the floor.
"Brains... Jill sandwich... brains..."