Recommended
The Twinkling Light Set: An increasingly rare but delightful type of decorative lighting
Why people recommend it
Technology Connections is credited with a good explanation of how old Christmas lights flash without any circuit, showing how simple the mechanism is.
Watch for: Only the first half covers the flashing bulbs
In their words
The Technology Connections video explains it well.
TRiG on electronics.stackexchange.com, Dec 2021. CC BY-SA.