Gold Is Where You Leave It - S1-E19
Revealing mistake: Buck lights the fuse and tosses the dynamite-filled barrel at the bad guys. We see the explosion. Unfortunately, after that, we can also see the intact barrel still rolling away in the dirt.
A. B. and C. - S1-E3
Revealing mistake: In the fight at the end of the B scenario, Number 6 has a small problem. His pants split open in the back. Fortunately, they somehow manage to mend themselves again.
Revealing mistake: As Delta Tango 19 takes off from the airport, there is a shot where it is actually landing. This can be seen from the fact that there is no runway behind them, as it is in front of them.
Revealing mistake: A chalk outline on the parking garage wall where the actor playing the alien that just got shot and disintegrates is supposed to place his body and limbs for the special effects (the disintegration) is visible. The actor placed his body just outside the chalk outline, and the arms were not in the correct positions.