It is a phrase used in his native Holland that describes the holy grail of all scouts, the nugget of gold just waiting to be discovered that no one has spotted the potential of.
Glenn appointed Theo earlier in the year until the summer to tap into his knowledge of football on the continent.
And he has more recently augmented his network of scouts by bringing in Paul Montgomery, who was previously at Newcastle and Derby and has spotted the talent of, amongst others, Laurent Robert, Jermaine Jenas, former Hammers Paolo Wanchope and Igor Stimac, and Rory Delap.
Says Glenn Roeder:
"I have known him for many years; Jim Smith took him to Derby and worked with him for a number of years, and in the last few years since Bobby Robson has been at Newcastle he has been working for his home town team.
"But I have managed to prise him away because our friendship goes back a long while, and his track record of unearthing good players has been very good down the years.
"Having worked for Jim Smith, who never had a fortune to spend in the transfer market, he has unearthed several excellent players for Jim.
"He is definitely a person who has got a good eye, and to give you an example he told me about the Mpenza brothers when they were 16 or 17 playing in Belgium.
"One of them, Emil, is a top drawer striker with Schalke and the number one striker in Belgium.
"I am very pleased to have him on board; he has been with us a month or so now and we have him all over Europe, compiling a list of possible players for us to look at between now and the end of the season and in the summer.
"We are putting a fair bit of money into our scouting system because we are trying really hard to unearth players before they become well known, because once they are known to the big clubs in Europe they become so expensive and we can't afford them.
"We need to discover them before they have that big move, and we are trying to find younger players as well.
"We want to get away from signing too many players that are into their 30s although I have to say overall in the last few years there has still been room for one of those players to be at the club; we have been very successful with the likes of Stuart Pearce, Nigel Winterburn, and Ian Wright who scored goals when he first came here.
"There is still a place for older players for a season or two but generally speaking it would be nice to unearth some young talent, which is what we are trying to do."
Hence the miles being clocked up by Paul and Theo Vonk, who says:
"I travel across Europe but especially Holland, Germany, Belgium, the Czech Republic, and Scandinavia."
"I meet many other scouts from England and after a few months they become familiar with them, and sometimes chief scout Ted Pearce, and scout Kevin Bond come over to see a player as well."
Theo, who comes recommended by Romeo Zondervan, who holds a similar position with Ipswich, adds:
"Everybody is looking across Europe for what we call 'the golden chicken'; not just the clubs, but the agents as well, who have their own scouting system."
54 year old Theo, father of former Manchester City defender Michael, has his work cut out at the moment as the search for a loan player intensifies, and he says:
"Mostly I communicate with Ted Pearce and he talks to Glenn; at the beginning of the week we make the planning for the whole week and on average I see four or five games a week.
"I fax my reports every Monday morning to Ted and sometimes I go to England.
"I have mentioned several players who are in my opinion suitable for the Premiership but often it is a matter of money.
"I give the technical advice but of course the ultimate decision is down to Glenn; I know every player in Holland, Belgium, and Germany, and there are several good ones, but I don't interfere in negotiations.
"After looking at a player four or five times a decision has to be made; I particularly look at whether they could adapt to English football or not."
Theo, a former central defender, certainly has the experience to spot a player; he was a professional for 13 years, and was in management for 22 years in Holland and Spain in an association that spanned nine clubs.
"West Ham need someone for the rest of the season and I have to know everything about a player that is a target," he explains.
"I make my own squad and in every position I have three or four names but then it is a matter of money.
"We are looking for some Bosman players; there are some good ones around this summer and we have been monitoring them.
"The last five or 10 years the business side of it and the money for the players has increased incredibly, but I think the high salaries will become less in the future.
"But, compared with England, the players in Holland and Belgium don't earn so much."
Glenn Roeder adds:
"Theo is very busy at the moment; obviously Holland is his back yard and we are trying to get as much knowledge as we can about the players in that part of the world at the smaller clubs."