"Flesh" is a collective noun, which means it represents a group of something. It is always singular.
Here's how you might use "flesh" in a sentence:
* "The lion sank its teeth into the flesh of its prey."
* "The artist painted the human flesh in exquisite detail."
If you want to talk about multiple pieces of flesh, you would use "pieces of flesh" or another phrase to convey that.
Let me know if you have any other questions!