If you give a cat enough time, it will assume the shape of whatever box, jar, or sink that contains it. According to this definition of liquid – a substance that flows freely, but is of constant volume – cats are indeed a liquid. At the very least, they’re a non-Newtonian solid.
For the science behind this question, see this article on rheology.
And since we are on the subject of liquids… this week we’re making edible water bottles using sodium alginate and calcium lactate. Based on what you can find out about water, can you predict the shape of the container you are making to store it?
The instructions for this project are in the bag of supplies at the library.