Who sees Don John as the probable cause of the problem between Claudio and Hero at the wedding in Act Four and what does that show about him?
Benedick is the perceptive character who immediately suspects Don John as the culprit in the plot. The exact lines are as follows:
There is some strange misprision in the princes.
Two of them have the very bent of honour;
And if their wisdoms be misled in this,
The practise of it lives in John the bastard,
Whose spirits toil in frame of villanies.*
This correct assumption of Benedick's shows that he is a more rational and less emotional man than either of his friend's. He is sound in his judgement, wise, and not likely to be easily biased or overwhelmed by his situation.