No Sound on ONE Facebook video. Works on iPad.

OK, this is a weird one. I shared a video that came up in my Facebook newsfeed while I was on my iPad. Today, my dad was in Facebook in Safari on his Mac and when the video begins it has sound, then it mutes after a few seconds. I have tried and tried to get it to play, checked the sound settings in the System Prefs, in Safari, and on Facebook. Nothing works. Every other video I try works fine.

So I went back to the iPad and ran the video. Worked fine. Tried it on my Mac in Safari. No sound. This is really driving me batty. Any ideas?