Another palette knife painting, but not the eyes or whiskers - I did those with brushes. The whiskers were the attraction of this subject, as well as the thing I feared. I cannot say how many hours I have spent practising whiskers. A lot. I have probably bought a dozen or more brushes specifically for the purpose.
As well as what tool to use, the other problem with whiskers is the need to have a nice, relaxed hand. As soon as you tense up, the wobble-problem begins and the whisker ends up more zig-zag than a nice sweeping curve. But it is difficult not to tense up. Whiskers are like going to the dentist: just relax, they say. Relax?? HA.
Here is a summary of my various attempts:
Soft flat brushes, used on their sides and chisel-edged: feasible but difficult to create super long whiskers using this method. Mine tended to get fatter near to the ends instead of thinner
Sable round brushes: good for short whiskers. They run out of paint for long ones and cheap brushes start to splay so you get the "fat end" problem
Teeny-tiny brushes, meant for miniature work: only good for super short bristle type whiskers. They either run out of paint for long ones or the whisker goes wobbly
Palette knife on its side: good for a representation of a whisker but you can't produce a nice curve so this method has its limitations
Riggers of various sizes: I used a number 3 for most of the whiskers on this cat. The consistency of the paint has to be just right. I have a practice board to hand and mix white with mineral spirits and maybe a tiny bit of Liquin - not too much or it will make the paint translucent which is no good for a nice, firm whisker - and practice on the spare board until the consistency is right
If I get it right, I avoid blobs along the whisker (not a good look) or running out of paint or producing big fat chunky whiskers or producing whiskers that look like they are draped with cobwebs.
If I get it wrong, well I have to wipe it off.
Which brings me to my show-stopping conclusion: don't put whiskers on your cat until your cat is dry. Then, you can scorn defiance at blobs or wonks or splats and simply wipe them off.