Been using this one a lot recently with exciting results.
On any sustained, formed vowel – like an ah, oh, ay, or an ee, I have the singers make a claw with one hand, and hold it directly in front of the mouth. The hand shape is the same one you’d use if you were pretending to be a scary lion – except that the curved fingers are facing towards your mouth.
If you’ve never pretended to be a lion, but know a little about baseball, it’s also pretty close to the hand position for throwing a knuckle ball (again with fingers towards the mouth).
This works very well on the ends of phrases to help the chorus really lock in a big, bright chord – especially if in addition to the claw, the singers also think slightly nasty/mean thoughts.
As with many other physical techniques that can’t be used on the performance stage, once the singers have learned how they feel, and once the effect has been incorporated into body memory, we can get the same results when I use a more subtle version in front of them as they sing.