**Core Concept**
Experimental trials, also known as randomized controlled trials (RCTs), are a type of clinical research study designed to evaluate the efficacy and safety of a new treatment or intervention. In animal trials, researchers often use double-blinding to minimize bias and ensure the accuracy of the results. However, due to the nature of animal models, double-blinding is not always feasible.

**Why the Correct Answer is Right**
The correct answer is **A** because double-blinding in animal trials is challenging due to the complexity of the experimental design and the need for direct observation of the animal's behavior. While it is possible to use blinding techniques in animal trials, such as hiding the treatment allocation from the researcher or using a blinded observer, it is often not practical or necessary. This is in contrast to human trials, where double-blinding is a crucial component of RCTs to minimize bias and ensure the integrity of the results.

**Why Each Wrong Option is Incorrect**
**Option B:** All animal trials are not unethical. In fact, animal trials are an essential part of the preclinical research process, allowing researchers to test the safety and efficacy of new treatments before moving to human trials.

**Option C:** It is possible to do interim analysis in experimental trials, including animal trials. In fact, interim analysis is often used to assess the trial's progress and make decisions about continuing or stopping the trial early.

**Option D:** Experimental trials are not always prospective. While prospective trials involve enrolling participants before the outcome of interest has occurred, retrospective trials involve analyzing data from past events or outcomes.

**Clinical Pearl / High-Yield Fact**
When designing an experimental trial, researchers should carefully consider the feasibility of double-blinding and other bias-reducing techniques, taking into account the specific research question, study design, and experimental model.

**✓ Correct Answer: A. Can’t double blind in animal trials**