Animals do not sin because they are not at enmity with God. A sin is breaking God's law intentionally and willfully with hatred for their Creator. Read Romans 8
Originally Posted by Scottizzle
Grace to you
If we doubt or do not believe that God is gracious to us and is pleased with us, or if we presumptuously expect to please Him only through and after our works, then it is all pure deception, outwardly honoring God, but inwardly setting up self as a false [savior].... (Part X. XI) Excerpts from Martin Luther, Treatise Concerning Good Works (1520).