parsha bit: Chukat

The torah tells us that when the people rebelled and demanded water, Moshe struck the rock twice. Why twice? He hit it once and a trickle of water came out. The people mocked him, saying "is that all you can do?" At that he became angry and struck the rock a second time, and enough water gushed out to push things out of its path. (Tanchuma, Chukat 9)