As Billy looked in shock as his hands slowly grew it was soon followed with his body following suit by making him grow to 6'3" and gaining some muscles.
While this was happening Jenn crouched grabbing onto her stomach as she regretted consuming as much water as she could which was 4L. She collapsed to the ground at nearly the same time as Billy did.
But what happened to her was that a dark scaley tail ripped through her skin to the outside world to grow in length to 6"4' as scales spread across her skin her hair changed into tentacles as it lengthened to the base of her back. And finally her tongue split.
When the changes finished they both looked themselves over, Billy who was 21 and 6'3" with some muscles. And Jenny who was a 6'7" anthro lizard.