Over in this neck of the woods, we are rightly proud of local lad Percy Shaw (1890–1976), the inventor of the catseye, which has saved untold lives on the nation's roads.
It is said that Shaw's invention was inspired by seeing light reflected off a cat's retina at nighttime.
It turns out that Percy Shaw wasn't the first man of science to investigate reflections from cats' retinas. This from The Eye: a Natural History by Simon Ings (pp.184–5):
In 1703, [French anatomist Jean] Mery noted that a cat's eyes shine much more brightly if you hold the cat underwater…
[W]ell over a century after Mery dunked his cat, [Swedish-born naturalist, Karl Asmund] Rudolphi turned his attention to the directionality of the shining eye. He was able to show that the reflecting eye will emit light along exactly the same line as the direction of the in-going rays. No chemical or biological process is taking place—a point he demonstrated by the simple expedient of shining lights into the eyes of a decapitated cat.
That's the way to do it.