You can tell a lot about a person’s skills by how they utilize hills. Do they unnecessarily step on the brakes when going downhill? If so, when do they let off? …Or, do they accelerate or use gravity and their momentum when going downhill in order to help propel them up the other side?
(Of course, getting an accurate ‘reading’ of their skills requires taking their full surroundings into consideration, which requires more ‘reading traffic’ from you.)