When an engine is ignited, it produces thrust and boosts the rocket into the sky. After the propellant is used up, delay is activated, producing tracking smoke and allowing the rocket a brief coast.
infirmary (plural infirmaries) 1  A place where sick or injured people are cared for, especially a small hospital; sickhouse. 2  A clinic or dispensary within another institution.
Ulcer is a catch-all term for any hole in a bodily membrane. In the case of canker sores, the top layer of epithelial cells gets worn away, exposing the blood vessels and sensitive nerves underneath. Think of it like a blister with its outer dome dissolved.