Help me figure out density column, please?

For chemistry cl, I have to figure out the composition of a four layer density column. The bottom layer is corn syrup, the third is water with red food coloring, the second is vegetable oil, and I can't figure out the first. Wrong guesses so far: distilled water, contact solution, nail polish remover, and I don't remember any of the others. What is less dense than vegetable oil that is a clear liquid? The teacher told us that if we drank the entire column, we would be uncomfortable, but definitely wouldn't die. So that rules out any dangerous chemicals, and we are juniors in high school in Utah so the teacher wouldn't have used anything we don't know the name of. Thanks in advance for your help!!!