1. The balloon inflator left in the background. We made sure to remove it after this shot.

2. Over Exposure. We adjusted for this throughout our trials with the timing of the release of the camera shutter relative to the timing of the explosion, and by the end we had very good exposure.

3. The pendulum hadn't moved. We guessed (correctly) that this was because both flashes went off before it had moved, meaning the delay for the second flash was too short. We corrected this by adjusting the delay longer, and later changing to a lighter pendulum.

4. The strange streaks. We discovered that these were scratches on the Plexiglas we had in front of the camera refracting the light. We decided after a few trials that the Plexiglas was unneeded anyway, so we removed it.