This is the New Age Sensitive Plant (Mimosa pudica). It is one of the few plants that moves at speeds that human beings can appreciate. If touched, the leaflets immediately fold up, and if touched again, the stems go limp.

They are common on rough ground in Lamma - here are three pics taken around Pak Kok.

<img src="http://www.compunicate.com/Lamma/27/mimosa1-bb.jpg" border=1>

Before touching:
<img src="http://www.compunicate.com/Lamma/27/mimosa2-bb.jpg" border=1>

After touching:
<img src="http://www.compunicate.com/Lamma/27/mimosa3-bb.jpg" border=1>

For more botanical details - see

http://www.comfsm.fm/~dleeling/angio/mimosa.html