"pretend I did not understand English very well."

This is a good way to get ourselves away of some things we do improper or weird in public, not on vicious purpose though: if I were caught by a police officer because of speeding or something  

If it is not in my earshot, seeing 2 women chat in a low voice almost like whispering and laugh out loud  I would be curious about what exactly they chat about, so to intend to "overhear"them instead of the obvious eavesdropping I would approach them quietly as I adjust my facial expression into a poker face pretending I don't understand English.