'''Basic Trope:''' A seemingly insignificant change in the past causes disastrous results in the present.
* '''Straight:''' Bob travels back in time and accidentally kills a butterfly. As he returns to the present he finds that it has become a grim CrapsackWorld where humans are barely surviving.
* '''Exaggerated:''' As soon as Bob materializes in the past, he instantly disintegrates because his arrival has dislodged a tiny grain of sand that caused all life on Earth to be wiped out at some point in less distant past.
* '''Downplayed''': CloseEnoughTimeline
* '''Justified''': Every small thing plays a significant role in the natural course of events, so changing one of these things will change the course of events.
* '''Inverted:''' [[MergedReality Bob travels back in time and accidentally kills a butterfly. When he returns to the present, he finds it to be a beautiful]] CrystalSpiresAndTogas [[MergedReality utopia, with technology centuries beyond what he knew.]]
* '''Subverted:''' As Bob returns to the present, he is horrified at what he sees and then [[MyGodWhatHaveIDone is shocked as he remembers a butterfly he had accidentally killed]]. However, it turns out that these images and feelings were simply hallucinations caused by side effects of time travel.
* '''Double Subverted:''' ...But then it turns out that these "hallucinations" were actually signs of the DelayedRippleEffect.
* '''Parodied''': Bob stepped on a butterfly in the past, which leads to butterflies taking over the world.
* '''Zig Zagged''': As above, but it turned out he had just landed in the butterfly exhibit of the zoo...and then the moths come in and escort him to ''his'' cage.
* '''Averted:''' [[InSpiteOfANail Bob travels back in time and accidentally kills a butterfly. When he returns to the present, nothing has changed.]]
* '''Enforced''': "Hey, we need a filler episode to pad out this season. Let's let Bob screw with time travel."
* '''Lampshaded''': "All I did was step on a butterfly. How did all this happen?"
* '''Invoked''': Bob wants to destroy the world, so goes back in time and kills every butterfly he sees.
* '''Exploited''': [[FemmeFatale Alice]], knowing that Bob is [[IdiotHero a moron]], tricks Bob into going back in time, causing [[GambitRoulette a chain of events which inexplicably leads to Alice ruling the world.]]
* '''Defied''': Bob takes great care not to disrupt anything while in the past, especially butterflies.
* '''Discussed''': "Be careful. One little change here can destroy the Earth in the future."
* '''Conversed''': "Bob just stepped on a butterfly. That can't be good."
Back to ButterflyOfDoom. Be careful not to step on anyth-- [[BigNo NOOOOO!!!]]