One of many odd characters in a Samuel Beckett novel carried around an exact number of pebbles in his pockets and was constantly transferring them across from one side to the other. And Captain Queeg in The Caine Mutiny had a similar habit with ball bearings that clicked as he fiddled with them.
The Stonechat is the closest we get to this kind of obsession on Blacka. His call is just like two pebbles clicking. This compulsive habit is also a good test of the effectiveness of hearing aids on ageing bird watchers.