Either,
1. The darkness and other plagues; which obeyed God's word, and instantly came at God's call. So this may be a reflection upon the Egyptians, that those brutish or unreasonable creatures were more obedient to the will and command of God than they were. Thus diseases are said to come or go at God's command, Matthew 8:8. Or rather,
2. Moses and Aaron, mentioned Psalms 105:26, and called they, Psalms 105:27, whose obedience in denouncing and inflicting these plagues, and especially that plague of darkness, is noted and commended here as an act of great faith and fortitude, because they inflicted that plague after Pharaoh had threatened them, Exodus 10:10; as the obedience of their parents is commended as a great act of faith, because they preserved and hid their son contrary to the express command of the king of Egypt.