on (one's) hands and knees
1. Literally, with one's hands and knees on the ground. I got down on my hands and knees to look for my contact lens. We crawled on our hands and knees to avoid breathing in the smoke from the fire.
2. In a show of supplication, submission, or humility. I had to go back on my hands and knees and beg for my old job back. With this weapon, the leaders of the world will be on their hands and knees before us!