Four subjects out of eight were seasick.

If the pill really does nothing -- These four were forordained to become seasick no matter what.

If you randomly draw 4 subjects from a pool of 8, what chance you get the 4 seasickness prone subjects?

This is an urn and ball problem: From an urn with 4 Silver (Seasick) balls and 4 Red (Resistant) balls, draw at random 4 balls; what probability the 4 red ones are drawn? If you randomly draw 4 of 8 to get the pill; what probability the 4 resistant subjects are drawn?

              First is red       4/8
              Second is red      3/7
              Third is red       2/6
              Fourth is red      1/5
              -----------------------
              Product            1/70