head-final content clause relativizer: it turns the current clause into a subordinate content clause, binds it to the {ke'a} pronoun, and restart the current clause afresh (as if its previous content was erased or moved into a hidden prenex).
x1 (event/state) implies / suggests / is circumstantial evidence for x2 (du'u); the probability that x2 is true, given x1, is greater than the probability without x1