When they heard (akouonte). Present active participle of akouw, while hearing. They were cut to the heart (dieprionto tai kardiai). See Romans 5:33 where the same word and form (imperfect passive of diapriw) is used of the effect of Peter's speech on the Sadducees. Here Stephen had sent a saw through the hearts of the Pharisees that rasped them to the bone. They gnashed on him with their teeth (ebrucon tou odonta ep auton). Imperfect (inchoative) active of brucw (Attic brukw), to bite with loud noise, to grind or gnash the teeth. Literally, They began to gnash their teeth at (ep) him (just like a pack of hungry, snarling wolves). Stephen knew that it meant death for him.