This image is a reference to a scene from the film "Spider-Man 2" where Spider-Man (performed by Tobey Maguire) stops a train using his superhero abilities; spider webs and super strength. This event causes him to lose a lot of his strength, and so he is carried through the now-saved train by the passengers, one of which says the phrase "carefully, he's a hero".
In this context, the phrase "carefully, he's a hero" is being used to compare the up-loader of the recent update's heroism and generosity to that of Spider-Man from the film Spider-Man 2.
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