Hello Nouveau Rose. First of all, thank you for taking the time to look at my sketches and write a critique.
I used a pen precisely because if I use a pencil I have the temptation to go back and erase and make it "perfect", instead of just trying to convey the pose and movement in the set time (in this case it was 1-2 minutes). Also, if I use a pencil I start drawing softly but soon I start drawing strong lines without realising it.
Next time I'll try using a pencil and I'll do as you suggested. Thank you for your advice.
The drawings are amazing, and the variety of colours adds a nice touch. The giraffe, bull, and hamster are my favourites.