A very funny bug in Amnesia.

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1. The tank has acid in it.
2. It bounces out of the tank.

Well, given that glass does not react to acid, and that the bottle is enclosed, I don't find it so strange. The bounces are a bit buggy (indeed), but I don't find the simple fact there are bounces any strange.

The bottle may be buoyant but it wouldn't fly up into the air over and over, especially when it lacks the momentum. It wasn't thrown in at high speeds; it was gently dropped in.

Although it is true it would need constant momentum to bounce up and down like that and in real life it would probably never actually leave the tank once dropped, acid (sulphuric acid anyway) is almost twice as dense as water, meaning it pushes objects away from it with greater force => greater buoyancy. Mythbusters actually proved it with quicksand (which is exactly 2 times denser than water); they took turns going into it and I remember Adam kept pushing Jamie into it and he just kept on bouncing back up (it was really interesting).

So, while the acid is buggy it would have bounced for a considerable amount of time I think.