  We study by computer simulation the "Hawkes process" that was proposed in a
recent paper by Crane and Sornette (Proc. Nat. Acad. Sci. USA 105, 15649
(2008)) as a plausible model for the dynamics of YouTube video viewing numbers.
We test the claims made there that robust identification is possible for
classes of dynamic response following activity bursts. Our simulated timeseries
for the Hawkes process indeed fall into the different categories predicted by
Crane and Sornette. However the Hawkes process gives a much narrower spread of
decay exponents than the YouTube data, suggesting limits to the universality of
the Hawkes-based analysis.
