Animal idioms:
1. Ants in one's pants: unable to sit still or remain calm out of nervousness or excitement
E. g. Lisa had ants in her pants the day before her interview.
2. Cat nap: a short sleep
E. g. I'm going to have a cat nap while you're cooking dinner.
3. Cat's got one's tongue: said about someone who doesn't speak (usually due to shyness)
E. g. It looks like the cat's got your tongue, Lucy. Are you always this quiet?
4. Chicken out: to decide not to do something out of fear (usually just before)
E. g. I was going to take a ride on Jack's motorcyle, but I chickened out when he gave me a helmet to wear.
5. Clam up: become quiet suddenly
E. g. Arthur clammed up when I asked him about his family.
6. Copy cat: a person who does the same thing as someone else
E. g. My sister is such a copy cat. First she bought the same car as me, and now she's applying to my school.
7. Dog days: very hot days
E. g. I sleep in the basement during the dog days of August.
8. Dropping like flies: dying/giving up quickly
E. g. My roses are dropping like flies in this early frost.