[Reverend Wright]

This says they they dumped the water in, then ran the film in reverse.

https://www.youtube.com/watch?v=4VHS3P6HW6Y

[frank ballenger]

Thanks for that film oddity video. My memory from probably 1973 wasn’t far off. Twice in the narration it says the film of water was turned upside down to look like it was flowing upward.

DeMille deleted the filmed frog plague scenes because they became unintentionally funny.
Did you see the movie Exodus: Gods and Kings (2014)?
The frog scenes has one jumping out of an Egyptian woman’s cupboard toward her face and others causing everyone to shriek and run around. Definitely humorous among the creepy scenes of blook in the Nile and impending death.