In 2014 Marc-Antoine Fardin, a physicist at the Paris Diderot University, tested the theory that cats are both solid and liquid using the principle of rheology, the branch of physics that deals with the flow of matter. This was based on the observation that while cats usually behave as a solid, they often adapt to the shape of the container they sit in, which is the common definition of a liquid (a liquid is 'the state in which matter maintains a fixed volume but adapts to the shape of its container').
The article was published as light relief in the Rheology Bulletin, but Marc-Antoine was this year awarded an ‘Ig Nobel Prize’ for his work. The Ig Nobel Prize is a parody of the Nobel Prize and honours 'research that makes people laugh, then think.’ Recipients are encouraged to attend the award ceremony in costumes that ‘honour the spirit of their research’ (we were disappointed to see that Dr Fardin was not dressed as a cat).
Dr Fadin can be seen accepting his award and explaining his research 33 minutes into the following video: