Never run to them trying to catch them. They will think you are playing chase and
run from you! 
If that happens to ours (a couple of times it has)....I either kneel down and say "treat" (and then pony one up) or go in the opposite direction running saying "come on, can you catch daddy?" which generally gets them to run to me.
The main thing is NOT to freak out...they sense that and get skiddish.
