what does someone mean if they said they don;'t eat anything sentient?

Answer 1

Vegetarians will use this line as well as "I won't eat anything with a face.
to be sentient is:
1. Having sense perception; conscious.
2. Experiencing sensation or feeling.
Data in Star Trek was a sentient being.

Answer 2

It means they are fooling themselves. Sentient means to be aware of pain, and there have been credible studies that show that plants react to being picked, cooked, or eaten.