Sabotage, 1935

Sabotage was a another of Alfred Hitchcock's thrillers. Made in the 1935, uses dramatic irony as a way of keeping the audience's attention and entertaining them. Dramatic irony is when some of the characters within the world of the film do not know specific details. However, we as the audience know everything. This is a way for us to both relate to the characters, and to sympathize with them.
With regards to this film, Stevie's sister's husband - Verlock - gives Stevie a package to deliver. Stevie must deliver the package, which contains a bomb, by half one. Stevie does not know of the bomb inside the package - this is an example of dramatic irony. Time passes, and Stevie becomes distracted, eventually leading to the bomb going off in Stevie's hands.

How Does Hitchcock Create Suspense and Tension?

There are several ways that Hitchcock creates suspense within the film. One of these ways is the use of the close-up shot. These shots allow the audience to witness the boy's facial expressions and emotions. Moreover, the shots of the package keep the audience thinking about it, and urge the viewer to feel sympathy for Stevie.
Additionally, Hitchcock uses contrapuntal music when the boy is in the market. To the boy, he is just wandering around the market, but as we know the package contains a bomb - thus the boy is wasting time.
Finally, as the scene nears its end, the music becomes more and more dramatic. This builds the tension, and places  the audience of the edge of their seat; the audience is expecting the bomb to go off.