Continuity mistake: During the song at the end, there is a zoomed out shot of the entire crowd. You can see Phineas and Candace both screaming with their hands in the air, their eyes closed, and Phineas is not holding a camera. When the camera instantly cuts to a close up of them, both of them have their mouths closed, their hands down, their eyes open, and Phineas is holding a camera.
Continuity mistake: In the scene where Doofensmirtz talks about how the sign blocks his view of other people's pain and misery, his window faces the sign. Then in the next shot where the laser blasts the sign, the Doofensmirtz evil inc. logo is facing the brick sign and the windows are facing the other way.
Plot hole: When Linda (Mom) gets home from her cooking class and greets the boys, she sees nothing out of place. However, just a few moments before, we see the giant laser in the corner of the yard that they forgot to attach to the laser-inator. Wouldn't she have seen this?
Continuity mistake: When Perry is tied to the firecracker he uses a laser watch to burn himself free, but in the next shot it's gone.
Continuity mistake: Near the end of the "Love Handel" concert the people in the audience switch from being close together to spread out leaving a path between shots.
Continuity mistake: During the song "Ain't Got Rhythm" Swampy's earring switches ears between shots.
Continuity mistake: During the end of the episode, Phineas is video taping his parents, but what he is recording is a different angle that what is being shown on the screen. From Phineas' angle, the camera is only showing the back of his mom's head. However, the big screen above the band shows that the camera angle can see both of his parents' faces.