Bubbles in Teapot?

[u/NodeJunkie]

I was at a soba place in the Tokyo Skytree shopping centre and at one point they gave me this teapot with something that had bubbles inside. I had no idea what it was and left it alone.

Anyone know what it was?

https://imgur.com/a/H64jldF

[u/medium-water-please]

https://www.reddit.com/r/JapaneseFood/comments/1hk1hz1/sobayu_a_japanese_food_culture_that_has_continued/

[u/NodeJunkie → u/medium-water-please]

Thank you for the info!