Learn Croatian: Nemoj se prejesti!

The prefix pre- often indicates doing an action to an excessive degree. When added to the base verb jesti (to eat), it creates the meaning of overeating.

Why do we need the reflexive pronoun se in this sentence?

While the base verb jesti is not reflexive, adding pre- to express doing something to excess usually makes the verb reflexive. You can think of it as doing the action too much to yourself, so the verb becomes prejesti se.

Why is prejesti in the infinitive form rather than an imperative (command) form?

Negative commands in Croatian are commonly formed using the helper word nemoj (for the singular informal you) followed by the infinitive. Because nemoj already expresses the negative command, the main verb prejesti stays in the infinitive.

Is prejesti se perfective or imperfective, and why does it matter here?

It is perfective. Adding a prefix to a base verb usually makes it perfective, focusing on the completion of the action. While negative commands often use imperfective verbs to forbid a general behavior, using the perfective here makes it a strong warning about a specific, immediate situation. If you were giving a general rule against a habit of overeating, you would use the imperfective equivalent prejedati se.