It was only a matter of time before the laws of nature caught up with a Christchurch prisoner.
A 24-year-old Christchurch Men's Prison inmate held out for five days in a "dry cell", but eventually passed 33 grams of cannabis hidden in his rectum.
Prison acting manager Trevor Saunders said the prisoner was locked in the cell, which did not have a toilet or basin, after he was suspected of concealing drugs.
Staff had seen him receive a package on February 28, and acting suspiciously.
"Those who are suspected of concealing contraband are placed in [a dry cell] to wait out the appearance of further evidence.
"During his time in the dry cell, the prisoner was determined not to pass any contraband. But it is only a matter of time before nature takes its course."
A total of 33 grams of cannabis and three grams of white powder, thought to be heroin, was discovered.
Saunders said the prisoner tried to fool staff into thinking he was hiding less by placing a small amount of cannabis on the floor.
"He obviously thought staff would think this was the entire amount and let him out of the cell. This was not the case, and after a couple more days the entire find was revealed."
The dry cell was used about once a month and the average stay for a prisoner suspected of concealing material was three to five days, he said.
The incident was one of three involving drugs at the prison in the past 11 days.
On March 4, a visitor was caught with a bottle of methadone and two valium tablets as she was approached by staff supervising the prison's metal detectors. Police arrested her.
"Behaviour like this will not be tolerated and I hope this acts as a deterrent to other visitors considering bringing in contraband," Saunders said.
In an incident this week, a tennis ball stuffed with 21 grams of cannabis and four ritalin tablets was found during a check of a unit's guttering.
"It seems the old drugs in the tennis ball is quite popular at the moment, with a few attempts at this over the last few months," Saunders said.