Why does my Chrome Extension crash YouTube?

Question

I wanted to program a Chrome Extension with JavaScript, that simply replaces the word "cat" with "dog" on websites. It works fine, however, I noticed that when I wanted to watch YouTube videos while the extension is running, the video won't play (Even though the words "cat" or "dog" don't appear in the HTML of the YouTube page. Do you know what might cause the problem or how I could fix my code?

Here is my code in the Content.js file:

document.body.innerHTML = document.body.innerHTML.replaceAll('cat', 'dog');

And here is the code from the manifest.json file:

{
"manifest_version": 2, 
"name": "DogsVSCats", 
"version": "1.0.0", 
"content_scripts": [
    {
        "matches": ["<all_urls>"], 
        "js": ["Content.js"]
    }
    ]
}

Thanks for any suggestions!