Presence of ambivalence. A character forced to make a difficult moral choice. Mystery or a puzzle to solve. A reminder of the stakes or increase stakes. Increase stakes of the character so that this is the only way they can succeed.
Situation is out of control.
A surprise or unexpected disaster. Any scene in which a danger is present. Any scene that has conflict in it. Any scene where a seduction occurs, or might occur. Technique of cutting back and forth between a dangerous scene and one that isn't dangerous.