The vampire looked scared...
He refused to cry again...
She pushed him off the cliff...
The footprints couldn't be human...
Only Mad Fred spotted the alien invasion...
Coming up with potential finishing lines is also a good exercise as it makes you think of what could have led to that point. All of the above examples could be used to finish a story too.
I see writing games as a great way to brain storm. I like to have brain storming sessions every now and again. When I've finished a novel or a load of short stories, I turn to ideas generated here and see if there is anything I could use for a competition or to trigger off another novel plot.
And the best thing about writing games is they are fun. They can be a morale booster too. In coming up with ideas for these, it confirms to you that you can write (and sometimes when your inner editor is being overtly critical of you, you could do with that confirmation - or at least I find that to be the case!).