The rat's inclusion in the game is a cute easter egg meant to showcase VR interaction possibilities. For the most part, Alyx is a masterpiece of gameplay and a trailblazer for the VR genre, and the inclusion of cutesy animals is always welcomed. Unfortunately, It didn't take players very long to find a way to turn a possibly cute interaction into an inevitably Cronenberg monstrosity when they found out the rats from City 17 to be much more stretchable than non-VR rats.
The poor rat will do a Plastic Man impression in different but equally horrifying ways depending on where you grab it. The world of Half-Life is already sad enough without having to throw rats as long as the snakes that eat them into the mix.