This is to demonstrate a close occurrence where San Ankou and Toi Toi may occur together, and when they do not.
San Ankou + Toi Toi
Tsumo: Open: 
The Tsumo on the 2-wan allows the 2-wan to count as the 3rd Ankou (closed triplet).
Toi Toi
Ron: Open:
The Ron on the 2-wan shows the 2-wan to count as a "pon" (open triplet). Thus, San Ankou does not count here.