Comment by aithrowawaycomm

Catchy headline, but also in a fluid in a dynamical sense - cats "flow" into spaces when exploring by trial-and-error testing openings with their body size, but they are also only "almost" liquid in that for especially narrow openings they are reluctant to poke their heads in, presumably because they might get stuck.

The contrast with dogs in the introduction is instructive: dogs tend to hunt over open fields rather than chasing prey into narrow dens, so it makes sense they would tend to make conservative eyeball judgments about whether they can fit into certain spaces. But cats will try to corner their prey in a tunnel/etc, so they have good reason to rely more on touch and experimentation ("ecologically-valid strategy").