I've spent 24 hours (when not at work / asleep) building a Cat-Splat entry. I didn't intend to do this next, but couldn't resist. We've just been trying it out - no cats so used the children - and it's a wee cracker.
This Lego nxt stuff is marvelous - so quick to reconfigure ...
Razorz51 was kind enough to say that Guard looked like a cat. Well, maybe it does, but it walks like a constipated dog. If you watch the video you'll see that it trips over it's own feet pretty often. What you won't see is that it also throws its gears off pretty often too.
My daughter is complaining about the bruises on her legs and arms - she fell off a chair trying to reset the thrower and simultaneously avoid getting hit by a flying ball. Unfortunately I didn't get video of my son trying to hit the balls with a cricket bat. Maybe next time.
This bot doesn't exactly splat, but I think it scores in terms of interacting with the domestic environment and getting noticed.
Note: design credit for this bot must go to David J. Perdue. I only built it from his instructions.