Here are a couple of more Easter Eggs from the Fringe episode "Subject 13".
The first is the video above, comparing the puzzle Walter frustrates young Olivia with, to the puzzle seen in the Alias episode "The Indicator". As you can see the puzzles are very similar, due in no small part to the fact that Fringe executive producer Jeff Pinkner also wrote that episode of Alias.
The second is a comparison of the Olivia "explosion" in "Subject 13" to another fire "incident" that we saw in the Fringe episode "Jacksonville":
|It's interesting to note that the fire does not come any where near young Nick. Either she unconsciously protected her Jacksonville experiment buddy, or he was immune to her powers because he was also a Cortexiphan kid.|
|The footage we see in "Jacksonville" is from a much younger Olivia than the one we see in "Subject 13"|
UPDATE: A couple of more interesting facts to ponder:
"Subject 13" was the first episode not to star Anna Torv. In fact, the only regular cast member in the episode was John Noble - no Anna Torv or Joshua Jackson (although we did see young Olivia and Peter). Plus no Jasika Nicole, Lance Reddick, Blair Brown, or even Gene.
According to the Fringepedia "death count" page, "Subject 13" was the first episode where no one died.