If "other" in a pulldown menu, any chance to have text box popup under to input the "other"?

If "Other" then provide opportunity for submitter to explain.

Any clues on how to do this?  (if possible here)

You can achieve this by adding a required Text Box field under that Drop Down field, and set up Conditional Logic to show the form field if Other is selected in the Drop Down.

Please take a look at images below for a visual guide:

Please let us know if you need further assistance.