Where I live milk comes in plastic bottles like this.
With a sealed lid like this
Now these seals are secure against tampering so why would several milk companies decide to add another layer of security to their milk? I assume it's because occasionally a few drips seep out if you lie a bottle on its side but this doesn't allow any way that the milk could be contaminated. So they have done this.
As you can see there is a firmly - very firmly - fixed cover which has a tab attached. This you are supposed to pull up to remove the cover. Looks nice and neat, doesn't it. Trouble is for those with arthritic fingers, carpal tunnel and any other grip problem as well as those with large or weak fingers this is impossible. We have to resort to sticking a knife or other sharp implement in and sawing the cover open. This means that not infrequently we - and the floor, bench top, cupboard doors - get splashed with milk.
At least there are a few companies still showing a modicum of sense but why cause a problem in the first place?