Nelson MP Nick Smith says he's "surprised" Renton has chosen to plead not guilty to the offensive behaviour charge.

A National party volunteer has described how a normal protest turned "freaky" when a woman lurched towards Nelson MP Nick Smith with rat poison.

"Nick's always surrounded by protesters [by the Saturday market] so I didn't immediately recognise this couple were anything out of the ordinary," Young Nat member Jonathan Subritzky said.

He said a woman approached Smith, while filming him, which seemed "a bit weird".

One of the helicopters involved in the poison drop at the Brook Waimarama Sanctuary.

“I’m standing in the door of the caravan and she starts shouting and saying; ‘How would you like some of this?'"

READ MORE:

* Three arrests as Brook Sanctuary poison drop in Nelson turns nasty

* Brook Sanctuary poison drop near Nelson runs 'smoothly' after arrests, sabotage

Subritzky said at that point the woman smeared rat poison on Smith's left shoulder, while a man she was with is threw poison pellets into the caravan, all while shouting abuse at them.

MARION VAN DIJK The Brook Waimarama Sanctuary is carrying out a poison drop to kill predators before native birds are reintroduced.

He said they were left with a packet of poison pellets which have now been given to the police.

The Brook Valley Community Group today suggested the incident near the Nelson Market on Saturday involved protesters motivated by something other than the controversial drop at the weekend.

Group chairman Christopher St Johanser was also sceptical about whether rat poison was involved.

However, Smith said he had no doubt what had prompted it.

"The man and woman who were involved in the incident made plain in their verbal comments that their action was consequential to the Brook Valley pest control operation," Smith said.

Smith said both he and other witnesses had given a statements to Nelson Police and he trusted they would "their diligent job".

"The situation became quite frightening when it escalated from verbal abuse and throwing rat poison at myself and volunteers to physical shoving and rubbing rat poison over my face and clothes," Smith said on Sunday.

He said police were called and the pair walked away "but continued threats to poison myself and my family".

Smith said he had never stated that the Brook Valley Community Group were responsible but said they needed to condemn it.

Police are investigating.

St Johanser said members of the group were not involved in the incident, but a member had witnessed it and her account differed from Smith's.

"It would appear that from the information given, and I stress this is hearsay, that the alleged reason for this alleged action was something quite other than protesting the poison drop," St Johanser said.

He said he was sceptical about the "assumption" it was rat poison.

He did not say what he understood the incident may have been about, but said the Brook Valley Community Group did not support such actions.

"What we shall say again, and this is something I've said on many many occasions . . . our community group does not plan, participate in, arrange or condone any unlawful activity by any person at any time, anywhere and for any reason."

St Johanser said a great deal of the group's effort focused on challenging the legality of actions taken by others, including the sanctuary trust, the Nelson City Council, an independent commissioner, owners of firms involved with the poison drop, and by Smith himself.

"All of these matters are before the Court as the subject of appeal," he said.

The controversial brodifacoum poison drop saw three arrests for trespass and a helicopter's fuel supply sabotaged on Saturday.

The sanctuary trust say the poison drop is a key step in creating a pest-free site.

Getting rid of pests would allow them to introduce rare bird species to the sanctuary.

Sanctuary general manager Hudson Dodd said the drop had gone smoothly and rainfall overnight hadn't caused problems.

He said the best practice guides for fine weather allowed for either six millimetres of rainfall or 10 millimetres of rainfall, depending on which guide you looked at, but they'd only had four millimetres overnight.

Dodd said he'd been grateful for support of volunteers who had checked the perimeter of the fence for bait pellets again yesterday, and were continuing to support the sanctuary's work.