How is the Shia prostration of thanksgiving performed?

One thing I noticed when praying in Iran is that many people perform an extra sujud (prostration) directly after the (Shia-style) taslim . It didn't seem obligatory as not everyone did it, but it seemed common practice. It looks like this is a *prostration of thanksgiving* (ref. ) which I had not encountered before going to Iran. I would like to know precisely how this is performed in case I decide to do this too. **Question**: How is the Shia prostration of thanksgiving performed? There appears to be differences, e.g., one does not perform the other parts of the rakat , but go straight into sujud from the sitting position.