Crunchy bits of deep-fried flour batter. てんかす、天かす。
Also called agedama. This is the same batter as used in making tempura. Small bits come of during the frying process and these are scooped out of the oil as otherwise they would start burning.
They can be re-used (and are sold separately for that purpose in supermarkets) by adding them to the soups of udon or soba, or sprinkled over cold udon noodles. Of course they fit well with tempura udon etc., but Tenkasu also can add taste quickly when there are little ingredients in the soup. But be careful not to be too liberal with them, as the taste soon gets oily.
[Tenkasu or agedama. Photo Ad Blankestijn]