Wow, pretty decent shot - through a cage *and* of an animal that probably moves a ton. Good work! (edit: and by "pretty decent" I mean I gave it a ten)
This little guy is so cute! I love his expression. I think what hurt you in this challenge was the bright area in front right more than anything - draws the eye away from Chilli.
Wow, you actually got the gerbil to stay still enough for this close-up! I know someone who has a gerbil and they are very active little critters. Love the details seen on this pet. He/she looks as if he/she is in it's cage/habitat which, unfortunately, acts as a distraction to the eye and takes focus away from the main subject. There is too much 'things' seen in the background and the foreground fares only a tad better with the slight blob of blurred bedding in the lower right hand corner. A simple and clean background (i.e. solid color or just nestled in the bedding) would help improve the picture because the gerbil would visually stand-out as the sole object of interest in the photo.