Plot hole: After stressing (as Waverly did earlier) that only a laser beam can activate the explosive crystals, LeGallows demonstrates the destructive power of one - using only sunlight. (00:37:15)
The Prisoner of Zalamar Affair - S1-E2
Revealing mistake: Mark finds the bomb planted under his Jeep and puts it under the bad guy's car instead. When it explodes, there's a huge cloud of smoke, but before the shot cuts, you can see that the car is completely undamaged. (00:10:30)