~そうに (apparent manner adverb)

The pattern [adjective stem]+そう+に, where そう attaches to an i-adjective stem (or na-adjective) to form a hearsay-or-appearance adverb — '[verb]ing in a way that looks/seems X.' 楽しそうに歌う ('sing in an apparently happy manner'), 嬉しそうに笑う ('laugh as if pleased'). Reports observable appearance, not certified inner state.