Facebook is experimenting with new ways to keep its users engaged, and is currently working on adding sounds to notifications and reply buttons to comments.

The social network is reportedly testing out the new features on small groups of users, and if all goes well the additions could soon be available to the masses. Getting a sound alert for notifications could be especially useful for mobile users, while the option of replying directly to comments to an original post would facilitate communication by offering multiple conversation threads.

"We are testing a new way to add comments to a post on Facebook," the social networking giant confirmed to VentureBeat. "With this test you will be able to reply to another comment as well as the original post. This is just a small test at this stage," explained a Facebook spokesperson.

The new "reply" button apparently sits on the right of the "Like" button on comments poster to a user's update, allowing people to start conversation threads off a comment. This would be particularly useful for posts with numerous comments where it's hard to keep track of who replies to whom. Facebook will notify members when another user replies to their comments, and will also show how many comments are in the reply threads.

VentureBeat was the first to report on the new reply feature after receiving a screenshot and link to the reply button spotted in the wild, as well as a link to a Thai blog that spotted it. The new reply feature seems to be available to members in several countries.

Meanwhile, the new notification sounds will make a ping each time users get a new like, comment, invite, or some other type of notification. Currently, when users get new notifications the notification icon simply turns red with the number, but there is no sound alert.

While hearing a sound for each notification may be useful for mobile users, for heavy users who get hundreds of notifications per day this new feature may be somewhat annoying. Meredith Chin, Facebook's Manager of Corporate Communications, has confirmed the new sound feature. Just as the reply feature, the sound notifications have rolled out only to a very limited number of users, and may or may not become permanent and available for everybody.

Users who are in the limited test group and find themselves annoyed by the sound notifications can turn off the feature. To do so, go to "Account Settings," select "Notifications," go to "How You Get Notifications," and un-check the box that says "Play a sound when each new notification is received."

VentureBeat's Sean Ludwig was among the small group of users to test the feature, and posted a video with the beeping notification in action. Check it out.

https://www.youtube.com/watch?feature=player_embedded&v=Oy1jW9M3ZRk