Atunguyrd - When a hole saw is used in a hand-held drill, it's almost inevitable that one tooth will break through before the others. Holding things dead perpendicular to the work piece is difficult. After the first break-through, a saw tooth can then catch on the edge of the cut. When it does, it will immediately stop the hole saw from turning, and all the motor's torque will be translated to the handles, trying to twist the drill out of your hands. The more powerful a hand drill you have, the more dangerous it can be, especially if you're blithely running at high speed and not anticipating the break-through. And of course, the larger the hole saw is, the more leverage it has! Been there, done that.