1.   He was in coma, and as he breathed he made a terrible bubbling sound.

2.   Also, it often makes a bubbling sound, something like water gurgling, while the heat is on.

3.   Suddenly we saw him lying unconscious on his side, with bloody foam coming out of his mouth making bubbling sounds.

4.   The group fell quiet, listening to the bubbling sound of their water pipes until George Assad, a friend, spoke up.