Other mistake: On the ship, Wall-E leaves dirtmarks everywhere, except when he's hiding behind an EVA pod. (00:37:20)
Other mistake: When Eve repairs Wall-E, she uses a jack to push him back into shape, putting it in one side, and separating it. Then she slides it to the other side. The jack collapses instantly as she slides it; if jacks collapsed that easily they wouldn't be very useful. The sort of jack she uses doesn't have a release mechanism either. (01:22:30)
Answer: It's a combination of what WALL-E sees happening to EVE, with her circuitry lighting up and her head bobbing up and down as she laughs, with the noise of the umbrella as the diagnostic arms try to force it down. All WALL-E can hear is something that resembles a mechanical screech, along with EVE reacting - he thinks that she's being electrocuted and is in pain.
Tailkinker ★