They were ducking because of the low canopy of the bushes and tree branches, and the giraffe wasn't just curious, it was chasing them. Have you seen how powerful a giraffe's neck is in combat?
the branches weren't that low or even in the path. and only the retarded looking bitch was ducking. She fears the giraffe is like Mr. Fantastic or Dhalsim.. Though, all three are gentle.