Sink or Float!
We played the Sink or Float game with Kimiko today and had a blast! Some of the things that float (due to differing density) surprised us quite a bit, and I think a few will get you as well. We suggest trying this one at home - and you don't really need an aquarium to do it! Just grab a large jar/bowl and a bunch of different items and have a blast!
Check out the video to see how we did it, and be as surprised as we were about potatoes -- and trolls!