The latest versions of Apple MacOS, and iOS include a video reaction feature which allows you to use hand gestures to add animated graphics to your screen! If you've been seeing balloons, confetti, or a thumbs-up bubble appear on your video you likely have this feature enabled.
Apple's informational guide on this feature can be found here.
Turn it on or off on MacOS
To enable/disable this feature on MacOS, click on the video menu icon which appears in the top right when a video call/live stream is in progress, then click on Reactions.
Turn it on or off on the iPhone
To enable/disable this feature on your iPhone, swipe down in the upper right-hand corner while a video call is active, and click on Video Effects.
Then, click on Reactions.