I see the game doesn't work after buying first upgrade and starting fight. Another issue I found is when losing all my health at stage 4, bought meat in the shop (which only restored a bit of that healt, so I had 2/5), and after leaving the shop I was getting "Thanks for playing" text, then going back to the shop.
This transition effect is so cool, but overused at the same time. Between every stage you need to wait for it to fold and unfold.
On my third attempt, I beaten the game. No upgrades, just my bare hands :D