  Sina Weibo, China's most popular microblogging platform, is currently used by
over $500M$ users and is considered to be a proxy of Chinese social life. In
this study, we contrast the discussions occurring on Sina Weibo and on Chinese
language Twitter in order to observe two different strands of Chinese culture:
people within China who use Sina Weibo with its government imposed restrictions
and those outside that are free to speak completely anonymously. We first
propose a simple ad-hoc algorithm to identify topics of Tweets and Weibo.
Different from previous works on micro-message topic detection, our algorithm
considers topics of the same contents but with different \#tags. Our algorithm
can also detect topics for Tweets and Weibos without any \#tags. Using a large
corpus of Weibo and Chinese language tweets, covering the period from January
$1$ to December $31$, $2012$, we obtain a list of topics using clustered \#tags
that we can then use to compare the two platforms. Surprisingly, we find that
there are no common entries among the Top $100$ most popular topics.
Furthermore, only $9.2\%$ of tweets correspond to the Top $1000$ topics on Sina
Weibo platform, and conversely only $4.4\%$ of weibos were found to discuss the
most popular Twitter topics. Our results reveal significant differences in
social attention on the two platforms, with most popular topics on Sina Weibo
relating to entertainment while most tweets corresponded to cultural or
political contents that is practically non existent in Sina Weibo.
