Oh wow...this is amazing...we learned how this can be done in chickens, which creeped me out (all I could think of was how the fast food industry and the chicken farmers were going to make all these mutant chickens with 6 wings...gross and totally possible…eww). It sounds like this is a pretty common birth defect, except for the fact that one arm is usually more developed, in this case both left arms seem equally under developed.