First, take a close look at both sides of the flour bag. One of the faces is very simple and the other is relatively complex. Turn the complex side, towards yourself.
Then take your scissors and, on the far left side of this complex face, make a cut to cut the line.
Withdraw the thread, and with a gentle tug, the entire complex seam, is pulled apart.
After the thread on this side is pulled to the far right, you can see the flourishes, but the thread on the reverse side is still on it, so it's time to go to the reverse side and remove it.
The thread on the reverse side is also very easy to remove, because it is a whole thread. After removing it, the flour sack is opened in one piece!
END
Note
Look carefully at both sides first
Look for the threads after you cut them