Identify the part of the sentence that contains an error in When I returned I felt (1) a big cat brush side me (2) as I opened the door. (3).

Introduction / Context:
This error spotting question checks correct verb object patterns and prepositional use in English. The sentence is divided into three parts followed by a No Error option. The scene describes someone returning and feeling a big cat move past them as they open the door. The task is to identify which part of the sentence is grammatically incorrect or unnatural in standard English usage.

Given Data / Assumptions:

The full sentence reads When I returned I felt a big cat brush side me as I opened the door.

Part 1 is When I returned I felt.

Part 2 is a big cat brush side me.

Part 3 is as I opened the door.

Part 4 indicates No Error.

The intended meaning is that the speaker physically felt a cat touch or pass by their side as they entered.

Concept / Approach:
The problematic phrase is brush side me. In natural English, we would typically say brush past me, brush against me, or brush by my side. The structure brush side me is incorrect because the noun side cannot directly follow brush without a preposition or possessive. The verb felt is correctly followed by the bare infinitive brush in this causative or sensory construction, so felt a big cat brush is fine. The error lies in the phrase side me, where a preposition such as past or against is missing. The rest of the sentence, including When I returned I felt and as I opened the door, is grammatically acceptable.

Step-by-Step Solution:
Step 1: Read the sentence smoothly and focus on the phrase a big cat brush side me, which sounds awkward. Step 2: Recall standard expressions like brush past me or brush against me that describe brief physical contact as something moves by. Step 3: Notice that side is a noun that usually appears in phrases like by my side or at my side, not directly after a verb without a preposition. Step 4: Recognise that a more natural version of the sentence would be I felt a big cat brush past me as I opened the door. Step 5: Conclude that the error occurs in part 2, because the phrase brush side me is grammatically faulty.

Verification / Alternative check:
Try repairing the sentence by changing only part 2. Replace a big cat brush side me with a big cat brush past me and read the full sentence: When I returned I felt a big cat brush past me as I opened the door. This is now correct and idiomatic. Another option would be brush against me, which also reads well. Both alternatives show that the original phrase side me needs a preposition or possessive form to be correct, such as by my side or at my side. Since the exam is concerned only with detecting the error, it is enough to identify that part 2 needs correction, even if the exact replacement is not requested.

Why Other Options Are Wrong:
Option A When I returned I felt uses correct past tense and introduces a sensory perception, which is grammatically sound. Option C as I opened the door correctly functions as a time clause describing when the sensation occurred. Option D No Error would mean that all parts are correct, but the unnatural and incorrect structure in part 2 proves that an error exists.

Common Pitfalls:
Students often read for overall meaning and may not notice slightly incorrect collocations if the sentence still makes some sense. Another pitfall is assuming that side can be used like beside without prepositions, which is not the case. In sensory verb constructions such as feel, see, or hear followed by an object and bare infinitive, it is easy to miss errors in the words that follow the infinitive. Training yourself to examine every word in such sequences and compare them with familiar expressions will help you catch subtle grammatical issues like this more reliably.

Final Answer:
2