Consciousness has a unique subjective feeling, which philosophers call 'what it is like' to experience something.

In 1974, philosopher Thomas Nagel wrote about what it is like to be a bat. He argued that even if we knew every physical fact about a bat's brain and sonar system, we still wouldn't know how it actually feels to be a bat. This subjective experience, like the taste of chocolate or the sting of a stubbed toe, cannot be fully captured by physical descriptions of brain cells.