How is the "light" trap at the beginning supposed to work?

How is the "light" trap at the beginning supposed to work? - Local person with bamboo fish traps

In the opening scene of Raiders of the Lost Ark, Indiana Jones encounters a trap where blocking a shaft of light with his hand causes spikes to shoot out of the wall next to him:

This always bugged me, as such a trap would probably require some kind of light sensor, which would be far too advanced for an ancient civilization to create.

Is there any plausible explanation for how this trap could work?






Pictures about "How is the "light" trap at the beginning supposed to work?"

How is the "light" trap at the beginning supposed to work? - Back view of anonymous person riding bicycle with huge bunch of traditional bamboo fish traps in countryside on summer day
How is the "light" trap at the beginning supposed to work? - Close-up Photography of Water Drops
How is the "light" trap at the beginning supposed to work? - Water Dew on Spider Web





How to Set up a Light Trap




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Images: Quang Nguyen Vinh, Quang Nguyen Vinh, Pixabay, Pixabay