I never knew this, as I have never experienced it, but occasionally when a baby’s teeth start to come through, a little bleeding may happen under the skin. It can create a little blood blister or bruise to appear on their gum. No treatment is usually necessary as it will disappear when the tooth comes through.
That said, it is recommended that, if your baby gets a teething blister and it is still there after a month and the tooth has still not come through you should take your baby to see your dentist.
Never prick teething blisters - this may cause an infection.
Some babies rub their gums together or "grind their teeth" as new teeth are growing and starting to come through. Be assured this is normal and its simply a way for them to relieve some of the discomfort caused by teething. Its also a way for them to explore their mouth and the changes which are happening.
In general, teeth grinding is normal teething babies and should stop when all the teeth have come through.