If I was confident in making the shot I probably would take it, but I have passed on that shot before because it didn't feel right. One thing I would be interested in knowing, what was it looking at? I have seen deer go alert like that because another deer, sometimes a nice buck, is coming in. Did you look to see what they were looking at? I've also had one do that and it be someone walking through the woods, missed a buck because they spooked it.