Why does the water in the toilet bubble then get sucked out?

Sounds like the vent's blocked and should be snaked from the lavatory roof vent. Put out enough snake to reach the base and 20 feet more to get out to the main or stack. Good luck, Tom

It is possible that the commode itself is partially stopped up, even thought you didn't mention that it was. When a commode is partially stopped the water will rise higher that it usually does and then it will start to syphon itself out till it breaks the syphon and then it will start to gurgle or maybe pubble like you said.

Letmetellu,
It's very doubtful that this will be a blocked drain. The bubbles or gurgles that she sees are caused by the toilet attempting to vent through the trap and suction will draw down the bowl level. If it were a partial back up the water would raise in the bowl and slowly seek its own level in the bowlas it drained out. Regards, Tom

Tom is 100% correct it is vent problem; check the main vent pipe. You quite probably have an obstruction which is giving you the soda straw effect. Put a straw in a coke, put your thumb on the top and remove it. The water will remain in it until you release your thumb (obstruction) and equalize the air pressure. IF you feel comfortable doing it, take a garden hose on the roof and chug the vent pipe until the obstruction is eliminated. You would be surprised what squirrels put in pipes, If not follow Tom's instruction, Good luck.

John