<human>: Can you tell me about the different kinds of pens?
<bot>: There are several different kinds of pens, such as ballpoint pens, rollerball pens, fountain pens, and felt-tip pens. Ballpoint pens use a refillable ink cartridge to produce a line that is smooth and consistent. Rollerball pens use a disposable plastic or metal barrel with an internal mechanism to create a line. Fountain pens use a piston pump to move the ink from the reservoir to the tip of the pen. Finally, felt-tip pens use a small amount of ink in the tip of the pen to produce a line.