14. The computer program product of claim 9 , where prompting the user for additional input includes modifying the search interface to include a menu with one or more items of suggested additional information.
9. A computer program product, encoded on a non-transitory computer-readable medium, operable to cause data processing apparatus to perform operations comprising: receiving, at a search interface, a first search query from a user; determining, based on a probability model of previous behavior of a collection of users, that the first search query is a trigger query, wherein the probability model is based on a probability of users of the collection of users selecting local search results in response to the first search query; in response to determining that the first search query is a trigger query, prompting the user for additional input, the prompting occurring prior to submission of the first search query to the search system; refining the first search query using the additional user input; and submitting the refined first search query to the search system.