Why are some bottles so hard to open?

[victor]

You can use the handle of a spoon to open ring pulls

[miasmum]

What I find the hardest are the rectangular boxes of washing pods, Bold Daz etc

[Suff]

They are an odd clip MM. You need to get your thumbs under the clip and push inwards and upwards. Real pain.

[Suff]

What I do not understand is that you can get two bottles of the same product from the same shelf and one is easy to open and the other is impossible - no matter with a tea towel or paper towel to help. I have a decent grip but even I need help.

Given that they are packaged by machines you do wonder. I do wonder if it is due to some of the liquid getting onto the top surface and bonding whereas some close clean. Never looked close enough.