These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Retroactive Recognition: Actually not very recognizable given that his face is mostly covered by flight gear, but that's Clint Eastwood who drops the bomb on the tarantula.
Special Effects Failure: The footage of the tarantula (which was a real one) is superimposed over that of sets and landscapes. As such, occasionally, you can see the spider reach the end of the film and fade out or (much more rarely) see through it. Mostly, though, it appears as an almost solid black mass.
And don't forget all the times when the monstrous tarantula roars and growls right before it eats someone.
What an Idiot: Okay, so the MadScientist has a plan to end world hunger by creating giant animals. So he tests his new serum on rabbits, guinea pigs, and a freaking tarantula?
Later on, The Hero finds a mystery substance on the ground. So what does he do? He tastes it.