Some friendships are held together by jokes nobody else could understand.

Long friendships build their own language. A phrase, a name, a reference to something that happened years ago becomes shorthand for an entire shared history, and using it says more than a paragraph of sincerity would. That is not shallowness. It is a record of time spent together, compressed into something small enough to carry.

If a friendship you value has gone quiet, you do not need to open with something profound. Send the joke, the old reference, the thing that will make no sense to anyone else. It reestablishes the fact of the shared past, and the real conversation gets easier from there.