Past & present tense together?

In all three examples the present and past tenses modify the objects, not the subjects, and are dependent on the context.

In the first example, it depends on whether "he" still thinks that dancing is a hard thing.

In the second example, it depends on whether the fishes can't or can now speak.

In the third example, it depends on whether "he" still needs to do something about it, or "he" has already done something about it.