Pencils actually do not contain any lead so you would not get sick from eating pencil lead or ingesting pencil lead.
Still pencils contain graphite which can make you sick though if you ingest it but it won't be as serious as lead poisoning.
If you do ingest enough graphite you may experience side effects such as stomach pain, coughing, vomiting, shortness of breath and even a possible bowel blockage.
Still you should avoid eating pencil graphite or chewing on graphite as it's not good for your teeth either and is a bad habit that you need to try to break.
Yes chewing on pencils is bad for you and the graphite in the pencils could make you sick if you happen to ingest the graphite.
There is no lead in the pencils though so you won't get lead poisoning but still it's never a good thing to chew on pencils because tooth damage can also occur.
Chewing on pens, pencils and many other hard objects can damage your teeth so it's never a good thing to chew on pens, pencils or anything else hard.
Chewing on pens and pencils or any other hard objects can wear down the edges of your teeth and cause your teeth to crack, fracture etc.
If you constantly chew on pens or pencils try keeping a carrot or other vegetable near you to grab to chew on which is much better for your teeth and for your health.
Chewing on pens is very harmful for your teeth as your teeth were not meant to bite down and chew on hard things like pens and pencils and cause cause tooth problems such as shifting, cracking, and breaking of the teeth, which can impair your ability to chew properly.