It's now a lot easier to include a reaction GIF into your Tumblr posts, like this a platypus getting tickled:
Tumblr just released a new feature that lets users search for GIFs as they post, making it easy to include a reaction GIF into a text post.
To add a GIF, click on the "+" button to the side of the text post box, and hover over to the GIF option. Currently, you can use this + button to add in photos or videos into posts.
The GIF will be automatically properly credited and everything. Boom. Easy.
Currently, this is only available on Tumblr for web, but the attribution and notifications will also work on the mobile apps.