premise: If the animal jumps out of the vehicle, or the truck is in an accident, the animal could be injured. 
hypothesis: The dog only broke its leg.
explanation_1: The animal mentioned in the first sentence could be anything, not necessarily a dog. The first sentence says that the animal could be injured not that it broke its leg which is what the second sentence states.
premise_logic: exists x1 x2 x3.(n_animal(x1) & n_animal(x1) & n_truck(x3) & n_vehicle(x2) & ((exists e1.(r_out(e1) & of(e1,x2) & Actor(e1,x1) & v_jump(e1)) | exists p1 x4.(in(x3,x4) & n_accident(x4))) -> exists e2 p2.(exists e3.(Theme(e3,x1) & v_injure(e3)) & Topic(e2,p2) & Actor(e2,x1) & v_could(e2))))
hypothesis_logic: exists e1 s1 x1 x2.(n_leg(x2) & of(x2,x1) & n_thing(x1) & n_dog(x1) & a_only(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_break(e1))
premise_sim: exists x1 x2 x3.(n_vehicle(x2) & n_truck(x3) & n_animal(x1) & (exists e2 p2.(v_could(e2) & exists e3.(v_injure(e3) & Theme(e3,x1)) & Topic(e2,p2) & Actor(e2,x1)) | all x4.(-n_accident(x4) | -in(x3,x4))) & (exists e2 p2.(v_could(e2) & exists e3.(v_injure(e3) & Theme(e3,x1)) & Topic(e2,p2) & Actor(e2,x1)) | all e1.(-v_jump(e1) | -r_out(e1) | -of(e1,x2) | -Actor(e1,x1))))
hypothesis_sim: exists e1 s1 x1 x2.(v_break(e1) & of(x2,x1) & n_thing(x1) & n_leg(x2) & n_dog(x1) & a_only(s1) & Theme(e1,x2) & Manner(e1,s1) & Actor(e1,x1))