The word "ear" is אוזן which also comes from the same root. If you are familiar with the Bible, often times the verb will be translated as "give ear". So, in a way, when you speak, you are "causing the other person to use his ears", or in other words to listen. Maybe the explanation is not perfect, but that is how I remember it.
Interesting. It's a helpful explanation and one that also reminds of the English expression 'to lend an ear'.
Poking around the internet, I found this small extract, which I've reworked for clarity's sake, to be helpful:
The הפעיל verbs are traditionally defined as the causative derivation of basic pa’al verbs: ברח means ‘fled' (lit. 'ran away') while its הפעיל cousin הבריח means ‘chased away’ (or ‘caused to run away’); אכל means ‘ate’ while its הפעיל cousin האכיל means ‘fed’ (or ‘caused to eat’); נכנס means ‘entered’ while its הפעיל cousin הכניס means ‘brought in’ (or ‘caused to enter’).
Here's the link to the academic paper in which I found the three examples: http://www.cogsci.ucsd.edu/~faucon/NILI/4.pdf