The following sentence has been split into four segments. Identify the segment that contains a grammatical error.

Every / curious child / want to / rip open a toy.

The correct answer is want to.

Step-by-step grammatical analysis:
1. Subject-Verb Agreement: In English grammar, the subject of a sentence must agree in number with its main verb.
2. Identify the Subject: The subject of the sentence is "Every curious child". The determiner "Every" refers to all members of a group considered individually, which makes it grammatically singular and requires a singular noun ("child") and a singular verb.
3. Identify the Verb: The verb used in the sentence is "want" (in the segment "want to"). "Want" is the plural/base form of the verb.
4. Find the Error: Since the subject ("Every curious child") is singular, the verb must also be singular. The singular form of the verb is "wants".
5. Correct Sentence: "Every curious child wants to rip open a toy."

Thus, the segment containing the grammatical error is "want to".