Wimping, whining and lack of effort mainly. You have to learn a lot in a short time, so ability to respond to instruction is important.
In answer to the original question, they can als0 backsquad you, which means you go back to day 1 and start all over again.
All of this can be avoided if you work hard, keep your ears open, your mouth shut and demonstrate that you really want to be a soldier. You do this by genuinely trying your best. And passing all the tests, physical, skill at arms etc.
You can get backtrooped if your not keeping up with your current troop or if not you can get UFAS'd(Unfit For Army Service) and discharged. Sometimes you can get back in after one of these but it depends on the circumstances. Go with a positive attitude and keep a sense of humour about you