Fred's instincts told him to place his hand over George's to try and hold his brother. But he didn't have the strength to move, and even if he did, he was hurting too much.
The song worked better at soothing his frayed nerves than any potion, however, and soon Fred closed his eyes. He wasn't about to fall asleep, though.
"I like this song," he said, giving his twin a serene smile.