Vision-language models (VLMs) have shown promising spatial reasoning capabilities from static visual inputs, where the evidence needed to answer a question is available in the provided views. However, in cluttered environments, answer-relevant evidence may be occluded rather than absent: an object may lie beneath a pile, be covered by another object, or have identifying information facing away from the camera. Answering such questions requires physical interaction to reveal the hidden evidence. We formalize this setting as Manipulation-Grounded Visual Question Answering (MG-VQA), where an agent answers a question about an initially cluttered scene by using manipulation as an intermediate evidence-gathering operation. We introduce MG-VQA-Bench, comprising 600 human-verified questions across four spatial reasoning tasks, and evaluate it in a cluttered tabletop interactive environment. Eight VLMs are evaluated under three levels of environment access: Direct (image only), Perception (pointing, segmentation, and scene graphs), and Manipulation (perception, grasping, and pushing). Across all models, Direct and Perception achieve average success rates of 36.2% and 37.6%, respectively, only slightly above an image-blind chance baseline of 32.7%. In contrast, Manipulation raises average success to 56.8% (40.8-83.0% across models). Stronger tool-calling VLMs, GPT~6~Astra (83.0%) and Gemini~3.8~Flash (69.3%), search persistently and re-ground after unsuccessful interactions, while weaker models often answer without gathering sufficient evidence or stop prematurely after failed actions. Our results highlight the need for VLM agents that use manipulation for persistent, physically grounded evidence gathering and recovery. Code and benchmark is available here: https://github.com/vineet2104/MG-VQA

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