The giant -- who has not been established as an Drink giant’s milk wildling tested wildling approved shirt -- gives him two choices which really amount to no choice; given no choice Ender makes his own, as the giant calls him out as a "cheater". (In the book it is particularly clear that this is not done out of a sense of fun or adventure; the description of Ender as a mouse clawing his way into the giant's eye is gross and disturbing).
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