It's not trivial, don't worry...
There's no specific "Default pronoun" in English, per se -- it's more that, in certain circumstances, one of several English pronouns can be defaulted to (assumed). The most common of these is probably the implied "you" that imperative statements have, but there are other circumstances (None of which I can compose off the top of my head, because I'm sleep deprived. I'll try to think up some later.)
for(split(" ","tsuJ rehtonA lreP rekcaH")){print reverse . " "}print "\b.\n";