Technical
MIKE GEORGE says:
This is what’s known as an articulated trigger.

The idea is that, when the gun recoils as you pull the back trigger, the front trigger can move forward so that it doesn’t bruise your finger.

The feature also helps you get at the back trigger if you have big hands with thick fingers, or if you are wearing thin gloves for winter shooting.

Don’t confuse this feature with other ‘push forward’ triggers.

If you push the trigger of a Baikal over-under forward, you select the top barrel to fire first.

A ‘push forward’ feature has also been adopted on some rifles, to operate a ‘set trigger’ mechanism.