Rodolphus had to admit he was a little impressed with Regulus' hiding place. He however was not impressed or even remotely pleased with his willingness to help Lucius. When he heard Regulus call out cheers to his little brother all he could do was glower at the the seeker.
What Rodolphus really wanted to do was knock the bottle away or break it somehow, he just could not figure out how. His normally quick wit and mind failing him. The bottle now having made it to his little brother before he could stop it in any way.