Underexposed and poor lighting with harsh shadows.
Although harsh and lacking any suggestion on how to fix, this is accurate...
These photos could greatly benefit from better lighting... Now if you are like me, you can't afford to shell out allot of $ for good lighting, so... we have to get creative... Try opening a window and getting some natural light on these guys... also, check out the strobist blog
Strobist: Lighting 101
There is allot of useful do-it-yourself stuff there. The poor lighting is what caused your harsh shadows, so fix the lighting, and your shadows with disappear.
As far as the background, it is a tad distracting, but I think working out the wrinkles combined with fixing the lighting could work wonders... I also think having an all white, or all black background could help too...
The expressions are priceless, and you have done a great job of capturing the animals personalities... In fact, I think the second photo could even benefit from a closer crop, because the expression is so cute...
Lastly, back to the lighting, play around with the flash... My best experience with an sb-series flash is to bounce the flash off the ceiling (if the ceiling is white!) and also have the subject facing an open window with sunlight falling on their face to remove direct shadows (under the eyes and on the face)... So... my advice... When you are shooting... Play around with the lighting allot and get a feel for what works with what you have... Keep shooting and Keep posting...