How to make tear material

Hi!
I want to create tear when my character cry. I saw someone made a good result from the material blueprint. But, I don’t quite understand what he meant when I read the comment. So, I would like to know how can I achieved the same result.
Here is the youtube video that I mentioned. Afterall: Character Tears / Cry - Unreal Engine 4 - YouTube

Thank you.

Hey. Did you ever figure it out?