
EDITING ESSAYS
578  Part Five  •  Other Grammar Concerns
 typhus, salmonella poisoning, and bubonic plague. (4) Rats have such 
huge appetites that it has been estimated that they destroy as much as 
one-third of humans’ food supplies every year. (5) It has been estimated 
that rats have been responsible for ten million deaths over the past cen-
tury alone. (6) Rats in the laboratory should probably be given credit for 
saving as many lives as wild rats have taken.
(7) Rats are used widely in laboratory research. (8) Rats have many 
similarities to humans. (9) Young rats are ticklish. (10) When a rat pup 
is gently scratched at certain spots, such as the nape of the neck, it will 
squeal. (11) The squeal can be heard only with an ultrasound scan. 
(12) The squeal has a similar soundgram pattern to that of a human 
giggle. (13) Rats can get addicted to the same drugs that humans do. 
(14) Rats crave alcohol, nicotine, amphetamine, and cocaine. (15) Rats 
can also overindulge. (16) They can continue consuming food or drugs 
until they die.
(17) Studies also show that rats, similar to humans, have personali-
ties. (18) They can be sad or cheerful depending on how they were raised 
and their circumstances. (19) Rats that have been raised in stable, caring 
conditions tend to be optimists. (20) Rats reared in uneven and unreli-
able conditions are likely to be pessimists. (21) Both types of rats can 
learn to connect a certain sound with getting food. (22) They also can 
associate another sound with no food. (23) However, when they hear a 
new sound, the two types of rats react differently. (24) The new sound is 
not associated with either food or no food. (25) The optimist will run to 
the food dispenser.  (26) It is expecting to be fed. (27) The pessimist will 
go somewhere else. (28) It is expecting nothing.
ANK_47574_32_ch32_pp563-581 r5 ko.indd   578ANK_47574_32_ch32_pp563-581 r5 ko.indd   578 10/29/08   10:21:26 AM10/29/08   10:21:26 AM