How do Sam and Eric describe the beast to ralph. Why do you think the description is so inaccurate ?

Their imaginations get away from them. All they really see is the silhouette of the dead pilot in the parachute yet they describe him as, "it is furry, it has eyes, teeth, claws, wings and it chased them". This description cements the fear within the boys of the beast as a real physical manifestation of their fears.