I messed up and bought the wrong interfacing for this project - I bought the sew-in kind. It would have still worked but I don't like to add extra steps to the process unless I have to. But it turned out to be a blessing because Connor decided he wanted his snake to be soft like his shirt. There are two places that creased up on me but it turned out not too badly. It was going to be a plain-jane, generic snake but a hood was requested and the cobra T-shirt was born.
He has worn it 2 days in a row now and hisses at everyone he sees.