An example is emoji responses. The fediverse has a significant Japanese community that barely overlaps with the Western communities. Besides a few large Mastodon servers, the Japanese community is much more likely to use MissKey (another microblogging platform).
MissKey allows for emoji response on posts. If a MissKey user sends an emoji response on a Mastodon post, the Mastodon user only sees that they got a 'favorite', while other MissKey users see the specific emoji.