"They heard someone shoot."

Translation: Ils ont entendu quelqu'un tirer.

[elli0777]

Why is tirer in the infinituve form here please, rather than "shooting" or "they heard that someone had shot"?

[Ripcurlgirl]

Because it follows another verb - entendre - conjugated in the passé composé. Whenever one verb follows another in a single statement (ie without a conjunction) the first may be conjugated but the second (and subsequent) verbs must stay in the infinitive.

[moonswooning]

Why does the entendre verb not agree with the ils?

[LavenderLover]

This lesson is concerning me with all the death and shooting

[Ripcurlgirl]

Then the evening news and the daily newspapers should disturb you greatly!