My teacher gave me a number of idioms with gaps to restore and understand it. I figured out some of them but others are unclear to me. Here are idioms with my suppositions:

1. to be gentle as a <sheep?>

2. to talk until the <cows?> come home

3. to be unable to say boo to a <?>

4. to have a <deer?> party

P.S. Above each idiom I have a little picture with an animal.