you can sell one of your models infinitely and i'm 100% sure this is a glitch
first click one of your models to bring up that little sell/cancel overlay
then click the mini sell icon behind the overlay
now click a different slot to move the model you just sold then click cancel
this seems to make the model into some ghost that has a few odd effects
like not letting you swap models around or tricking the game into thinking you never swapped out a model for battle
you can repeat the glitch on the same model over and over as long as you don't refresh the page
this lets you gain as many paws as you want and you can use them
by refreshing the page you'll update the game and any models you did the glitch with will vanish
and any paws you gained by using the glitch will vanish too
this might let you speedrun some achievements but i can't be bothered to keep track of that

if anything formats wrong i'm sorry i've never used a forum site in my entire life but i do like breaking games
and if this was reported before then idk man

Thank you for the report @Ragdoll I've sent this along to the Dev Team to investigate this!

EDIT: Looks like this is just a visual UI bug and does not appear to count towards gameplay or achievements. We will continue testing a bit more to be sure.