Why does whipped cream suck?

I love whipped cream. The canned kind.

But when I put milk, chocolate syrup, and whipped cream in a jar, cap it, then shake the jar, it sucks the lid on like it's vacuum packed.

This doesn't happen when I don't include the whipped cream.

So, how does adding whipped cream create a vacuum inside the jar?

It's mostly air, (Or nitrous) but if anything that gas should be at a slightly higher pressure than the air in the room. Otherwise the cream would collapse in on itself.

Most of the creme dissolves in the milk, but I would think the overall volume stays the same.

I don't think it has to do with temperature change, because if anything the expanding gas coming out of the can should be colder than the fridge. Mixing it with the milk should make it expand, and I fill the jar to the brim which should push out any warm air.

So why does adding the whipped cream make the jar vacuum seal itself?

I don't understand this. It seems impossible. But try it yourself, it's a real thing. It's absolutely magical.

by the way, It's also magically delicious and way easier than mixing with a spoon.
Why does whipped cream suck?
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