What is the test for probable cause when stopping a pedestrian for questioning?

'Circumstances short of probable cause may justify stopping a pedestrian for further investigation (citation), but before an officer detains an individual for questioning by means of physical force or a show of authority, he 'must be able to point to specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant that intrusion.' (Citation.)' (Cunha v. Superior Court, 2 Cal.3d 352, 355--356, 85 Cal.Rptr. 160, 162, 466 P.2d 704, 706.)