Indeed! "Otso" is a version of "ohto", which is also the original Finnish word for bear. The current word used in Standard Finnish is "karhu", which was one of the more than 100 euphemisms used instead of "ohto". Depending on the area you live in, about 3-20 of these words are still in everyday use. Of these, we currently also teach "nalle", which is these days used mainly of teddy bears. :)
If you have about 3-20 of these words in everyday use, are they interchangeable, or are there differences in nuance?
BTW, I want to echo what others have said -- thank you so much for working so hard and efficiently on this course. I was so surprised to see it in beta. Great surprise!