Try two fingers?

Carl thought since she seemed to be willing to let him go this far, why not try 2 fingers?

Carl withdrew his index finger, then pressed his two fingers against her butthole.

"Carl.. I think one is enough.. OWW!" Steffi shouted as he **** the second finger in.

"Carl stop, that hurts... just put the thermometer in now please...." Steffi whimpered.