The pronoun is not always expressed in the colloquial language, but its influence remains:
- Beth wyt ti'n (ei) feddwl?
- Beth ydych chi'n (ei) wneud?
where the mutations are caused whether the pronoun is there or not. In practice that is not always done in informal usage, or even always taught, but it is best to get in the habit if you want to speak and write Cymraeg da.
Welsh expresses it as "which superstitions are you in their believing" so the "eu" refers back to the superstitions.