the spider
Villeneuve says here https://youtu.be/2x-HaRcs2xQ that the spider "says something specific about sexuality and the subconscious of a man". note that he says spider, not spiders. dunno if that matters but I just noticed that.
here https://youtu.be/cVcPPs4ZVKkhe says this movie is "playful".
I think the size of the spider whenever it appears is very relevant. It's meant to mark perspective and proportion.