In this episode we get a bit of conflict between Hazel careful approach to problems and Bigwig's rush-headfirst-and-improvise-as-you-go-along attitude. It ends in Bigwig joining Efrafa (or at least pretending to do so). Here it's a rash decision that works out in the end, while in the book it is part of the carefully designed plan. Another difference is that in the book Bigwig is quite hesitant to play his role of secret agent in Efrafa. In the show he goes in without any doubts or anxiety.
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I find it funny that Hawkbit is chosen to go to Efrafa even though he is the last rabbit to volunteer, while Pipkin and Dandelion (who are first to raise their paws) get to stay behind. Lucky for them. They get credit for being the first to volunteer, but in the end they don't have to risk their lives.

: I don't see why he picked me. You put up your paw before I did.
I wonder about that thing too. Looking at this from Watsonian perspective, Hazel picks Hawkbit over Pipkin and Dandelion, because Pipkin is a child while Dandelion is one of the slowest rabbits in the warren (or at least that's what later episodes say). Fiver is slow too, but he has visions, so it's rational to take him on this mission.
Now, the Doylist answer would be that the group needs a pessimist to remind the audience how dangerous rabbits' quest is. Hawkbit usually having better/funnier lines would be another reason to include him in the group looking from producers' perspective.
