Amazing Tits

In the early 1900s, both Blue Tits and Robins had easy access to cream from the tops of open milk bottles left on doorsteps, and both birds imbibed.

After World War I, however, milk bottle tops began to be sealed with aluminum foil.  The Tits learned to pierced the foil to get at the cream, but the robins seemed incapable of learning the trick. 

The problem, it seems, is that tits are reared in flocks and learn by watching each other, while robins are solitary and territorial, and don't learn through mimicry. While an individual robin might learn to peck through the foil, other birds would not stop to watch to see how that was done.