Quick tip: using the image button (the expanding Mona Lisa) makes it easier for users to handle your images. Just drop in a URL, you can use Imgur to create one. Right click your uploaded image in Imgur and select "copy image address". And you don't need to blow them up first - just click on them to expand when they're in the post.
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I made a few edits, I hope you don't mind. They're just ideas, you may or may not like them. You gotta be true to your style.
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1: I turned the think bubble dots into mini clouds. I think this is a common way of representing 'thinking' so it could come across as more "readable". And it avoids the issue you had with removing the outline and leaving squares.
(You can probably make a much cleaner/nicer main think bubble. I just removed the internal outline, so it's a bit hard-looking.)
2: I added the glint to his right eye (the eye on the left.) I thought it looked a little odd just on one eye.
3: I tried to clean up that fist. I made a fist myself and saw that my hand only sticks out a lot on one side - the side with the thumb. So I removed most of the excess from the little-finger side, got rid of a few pixels that I thought weren't needed and tried to give the thumb a bit of definition.
4: The shirt sleeves looked like they were really pinching his arms to me. Ouch! I tried to add in a bit of excess cloth on both arms.
Like I say, just ideas. I don't normally work in 1-bit, but I just finished Gato Roboto so the 1-bit style is kinda fresh in my head and your images called to me. Interesting challenge, I may set myself more tasks in 1-bit.