The magical nail polish

My husband took home a bottle of transparent nail polish.
“Look, it can deter our son from bitting his fingers.” he said. “Really?” I said, and went through the instructions. It stated that the nail polish works on kids or adults to discourage them bitting their fingers by its distinct bitter taste. 
From that time on, my son grew a habit of biting his fingers often. I didn’t need to cut his nails from then on. Bonus? Good to me? Not really.
“ Honey ,can we...?” After being convinced, he allowed me to paint it on each of his little oddly shaped nails.
However, as a result, my son refused to have dinner any more that night after he used his bitter tasting fingers to pick a chicken wing and the taste was left in his mouth.
How awful must the taste be to make my son react like this? Out of curiosity, I painted my nails with it and licked it slightly. It had a extremely bad taste. You know, Chinese herb medicines have a very unpleasant taste. However, it's taste was even worse than the medicine's. After drinking tons of water, the bitterness has not gone away yet.
I made a complaint to my husband that the nail polish had an unwanted effect, stopping him from eating food. And even for me as an adult, it was not endurable . Therefore, I didn’t allow my husband to use it on my son any more since then.
Is there any better way to deter my boy from biting his fingers?