Pharaoh sent, and behold, there was not so much as one of the livestock of the Israelites dead. But the heart of Pharaoh was unyielding, and he did not let the people go.

“unyielding.” The Hebrew word is kabad (#03513 כָּבַד), meaning unyielding, hard, insensitive, stubborn, unresponsive, dull. See commentary on Exodus 4:21 and 10:1.