The One Big Happy strip from 8/21:
Ruthie, faced with the unfamiliar medical term the croup, does her best to assimilate it to what she knows, namely the ordinary-language term for a physical condition, the creeps. But this time, she guesses that croup is a portmanteau, of group and creeps.
From NOAD:
give someone the creeps: informal induce a feeling of revulsion or fear in someone.
And then from Wikipedia:
Croup, also known as laryngotracheobronchitis [AZ: !!], is a type of respiratory infection that is usually caused by a virus. The infection leads to swelling inside the trachea, which interferes with normal breathing and produces the classic symptoms of “barking” cough, stridor, and a hoarse voice. Fever and runny nose may also be present. These symptoms may be mild, moderate, or severe. Often it starts or is worse at night and normally lasts one to two days.
… Croup is a relatively common condition that affects about 15% of children at some point. It most commonly occurs between 6 months and 5 years of age
(In my experience, scary stuff in a baby.)