Christa Pike Felt Extreme Pain During Botched Execution, Death Penalty Expert Explains

Christa Pike experienced extreme pain during her botched execution in Tennessee because the drug administered to her by the state failed to knock her out and may have caused her to jerk around and foam at the mouth, according to a death penalty expert.

Deborah Denno, a 30-year professor at Fordham Law School whose articles on capital punishment have been cited by the U.S. Supreme Court, tells TMZ ... the whole objective in putting someone to death is to make sure the prisoner does not feel any pain during the execution -- and Tennessee failed big time on that front concerning Pike. 

In her case, Pike was administered two doses of Pentobarbital -- a barbiturate that acts as a central nervous depressant -- to carry out the state's lethal injection mandate, Denno tells us.

Denno says Pentobarbital can cause inmates to jerk around and foam at the mouth, even if they're unconscious.

According to Denno, prison staff pump the drug into a vein, which first acts as a sedative to render the inmate unconscious, "so you're not feeling what's going on and experiencing death."

But, in Pike's case, that didn't happen, Denno says, adding that the drug was "circulating just under the skin -- which can be extremely painful because it is a toxin."

Denno went on to say the drug was not seeping into Pike's system, which means that she was not getting a sufficient amount of it to kill her or render her unconscious.

Denno noted it should take less than 5 minutes to successfully carry out the execution with the inmate feeling no pain at all.

Clearly, the opposite was true in Pike's case ... she later told people that she felt as if her arm was about to burst during the failed execution.

As you know ... Pike was convicted of murder in 1996 for torturing and killing 19-year-old Collen Slemmer in Tennessee the year before. A judge sentenced Pike to death.