There is a common notion that pigeons and seagulls will explode if they eat Alka Seltzer (the same theory also exists about rice).
When Alka Seltzer comes into contact with liquid it releases carbon dioxide bubbles.
It is believed that pigeons (and most birds) are incapable of passing gas.
For this reason, the theory is that feeding a pigeon Alka Seltzer will cause their stomach to expand until they gruesomely explode.
Is It True?
Just because a bird doesn’t naturally pass gas this doesn’t mean that they can’t do it if neccessary.
A bird’s diet doesn’t typically contain foods that are likely to cause a build-up of gas hence birds haven’t been observed farting or burping. However, if they needed to it is very likely that they could.
Pigeons and birds in general routinely sick up food for their young to feed them.
If they can do this then they can easily regurgitate an Alka Seltzer tablet if they ingest it and realize they don’t like the experience.
Alka Seltzer will therefore not cause a pigeon to explode, all that will happen is they will be confused and disturbed by the fizzing and will quickly sick it up.