I cannot claim credit for the original idea for this. I saw it somewhere (on Pinterest maybe?) in a handwritten form and decided to create my own version. Students add details to the face (and hair if they wish). Then then cut out the tongue and write words with the "th" sound in them on the lines on the tongue. The tongue gets glued into the small oval on the face that they created so that it looks like a person sticking out his/her tongue.
This was a big hit with my first graders!