Well, I don't think it would not decide for one of them. So, there's a 50/50 chance? I am not sure, but if both are equal as good, then there's no point in making a weighted choice, so it's okey to choose whichever the donkey likes most, even if it's purely random. Perhaps a straw of hay points straight towards it and got his attention first, you can't focus on all straws of hay at the same time, so ...

Cheers