Fouille dans cette boîte !

Because this is an imperative sentence: it gives a command.

In French, the imperative usually does not include the subject pronoun. So:

• Tu fouilles dans cette boîte. = You are searching in this box.
• Fouille dans cette boîte ! = Search in this box!

So fouille here is the tu imperative form of fouiller.

That is a very common question.

With most -er verbs, the tu form of the imperative drops the final -s.

Compare:

• Present tense: tu fouilles
• Imperative: fouille !

The same thing happens with other common -er verbs:

• tu regardes → Regarde !
• tu parles → Parle !
• tu cherches → Cherche !

So fouille is correct.

Fouiller often means to search, to rummage through, or to dig through.

Depending on context, it can suggest:

• looking carefully for something
• moving things around while searching
• searching inside a container, bag, drawer, etc.

So in this sentence, it has the sense of rummage around in / search through the box.

Dans means in / inside.

So dans cette boîte means in this box or inside this box.

It is used because the action is happening inside the box. French often uses dans where English might say:

• in
• inside
• sometimes even through, depending on the verb

So Fouille dans cette boîte ! is literally something like Search inside this box!

Because boîte is a feminine singular noun.

The demonstrative adjectives are:

• ce for masculine singular before most consonants
• cet for masculine singular before a vowel or mute h
• cette for feminine singular
• ces for plural

Examples:

• ce livre = this book
• cet arbre = this tree
• cette boîte = this box
• ces boîtes = these boxes

So cette agrees with boîte.

Yes, boîte is feminine: une boîte.

That is why you get:

• cette boîte
• not ce boîte

In French, noun gender is something you usually learn together with the noun:

• une boîte = a box

That helps you remember its gender and choose the right article or adjective later.

The word boîte has a circumflex accent: î.

In modern French, this accent often does not drastically change pronunciation, but it is part of the correct spelling. Historically, it often shows that an older form of the word once had an s in it.

For learners, the main thing is simply:

• spell it boîte
• pronounce it roughly like bwat

So the accent matters mostly for correct writing.

A natural approximate pronunciation is:

Fouille dans cette boîte !
/fuj dɑ̃ sɛt bwat/

Very roughly for an English speaker:

• fouille ≈ foo-y
• dans ≈ nasal dahn
• cette ≈ set
• boîte ≈ bwat

A few notes:

• ou sounds like oo in food
• ill in fouille gives a y sound
• an in dans is nasal, not a full English an
• oi in boîte sounds like wa

It is informal singular.

Because fouille is the tu imperative, it is used when speaking to:

• one person
• informally

If you wanted to say it formally or to several people, you would use:

• Fouillez dans cette boîte !

So:

• Fouille ! = informal, one person
• Fouillez ! = formal one person, or plural

Yes, you could, and it would be understandable.

There is a small nuance:

• Fouille cette boîte ! = Search this box.
• Fouille dans cette boîte ! = Search in this box / Rummage through this box.

With dans, the sentence emphasizes the idea of looking inside it. Without dans, the box is treated more directly as the object being searched.

In everyday usage, both can work, but dans makes the spatial idea very clear.

Because this is a command, and French commonly writes commands with an exclamation mark.

It shows the sentence is not just a statement but an instruction, order, or strong prompt:

• Fouille dans cette boîte. = more neutral in writing
• Fouille dans cette boîte ! = clear command

So the exclamation mark fits the imperative very naturally.