Thought Jacob was Esau?

I encountered a problem similar to that of Isaac tonight. I've been away from home for 9 days. My oldest boy is 17, and the younger is 15, only 20 months younger. One of them answered the phone when I called home tonight, and I thought it was the older, William, but he pretended to be his brother Davis. Although it sounded like William, it was plausible to me, not being able to see them, that Davis could disguise his voice to be like that of William. Or because he'd been sick this weekend, it was possible his voice had changed. Or he could have matured, causing his voice to change and be more like his brother's. Therefore, I see how blind Isaac could have mistaken one son for the other.