Bunnies

Hello again, I hope that you are well.

I decided today to have a bit of change from the crochet and the doily making and decided to get out the old sewing machine. I have a bit of a soft spot for bunnies so attempted to make some really simple ones that would be suitable for both children and adults. 

They worked out quite well but on both of them the part under the arm keeps puckering up. I have no idea why this happens. It has also done the same around the tail and foot but not quite as bad. On one of them I used a felt backing and on the other a cotton backing. I initially thought that it was because the felt was too thick but when it happened on the other one as well I was well and truly stumped. 

Does anybody have any suggestions as to why this is happening?

PS. Apologies for the bad picture but the weather is still misbehaving.