1st if you laugh you downplay it, you are just curious what happened
2nd if shes trying to flake you even if she doesnt give you an anwser she knows that you noticed and that you wanted to know what happened
3rd you can make some conversation, maybe she has a good story or something ad you guys can talk and laugh about it.
4th if she anti-social she knows that she has someone who wants to be her friend and that it mattered when she didnt call.