1. A method performed by a data processing apparatus, comprising: identifying, based on stored search log data for user search activity of multiple users, a query pair including: a first query; and a second query that was received (i) within a specified time following receipt of the first query and (ii) from a same user as the first query; identifying user search sessions that each include both of the first query and the second query; determining, based on the user search activity, a number of the identified user search sessions in which a third query was received following receipt of the first query and the second query during a same user search session; identifying the third query as a follow-up query to the query pair based on a ratio between the number of the identified user search sessions in which the third query was received and a total number of the identified user search sessions that included both of the first query and the second query meeting a query suggestion threshold frequency; receiving the first query from a given user device; receiving, within the specified time of receiving the first query and from the given user device, the second query; and providing, to the given user device and in response to receiving the second query within the specified time of receiving the first query, data that present (i) search results for the second query and (ii) the third query at the given user device based on the third query having been identified as a follow-up query to the query pair.