C# Spinner

public static class Spinner

        {
            private readonly static Random Randomizer = new Random();
            public static string Spin(string content)
            {
                const char OPEN_BRACE = '{';
                const char CLOSE_BRACE = '}';
                const char DELIMITER = '|';
                var start = content.IndexOf(OPEN_BRACE);
                var end = content.IndexOf(CLOSE_BRACE);
                if (start == -1 && end == -1 || start == -1 || end < start)
                {
                    return content;
                }
                if (end == -1)
                {
                    throw new ArgumentException("Unbalanced brace.");
                }
                var substring = content.Substring(start + 1, content.Length - (start + 1));
                var rest = Spin(substring);
                end = rest.IndexOf(CLOSE_BRACE);
                if (end == -1)
                {
                    throw new ArgumentException("Unbalanced brace.");
                }
                var splits = rest.Substring(0, end).Split(DELIMITER);
                var item = splits[Randomizer.Next(0, splits.Length)];
                return content.Substring(0, start) + item + Spin(rest.Substring(end + 1, rest.Length - (end + 1)));
            }
        }

private void button11_Click(object sender, EventArgs e)
        {
            richTextBox4.Text = Spinner.Spin(richTextBox3.Text);
        }

 private string returnSpinnedPart(string part)
        {
            Random random = new Random();
            string[] values = part.Split('|');
            if (values.Length > 0)
                return values[random.Next(0, values.Length)];
            return "";
        }

        private string returnSpinnedContent(string input)
        {
            string spinned = input;
            try
            {
                Regex regexObj = new Regex(@"\{.*?\}", RegexOptions.Singleline);
                MatchCollection m = regexObj.Matches(input);
                foreach (Match match in m)
                {
                    string part = returnSpinnedPart(match.Value.Replace("{", "").Replace("}", ""));
                    spinned = spinned.Replace(match.Value, part);
                }
            }
            catch (ArgumentException ex)
            {
                MessageBox.Show("RegEx prob");
            }
            return spinned;
        }
        private void button12_Click(object sender, EventArgs e)
        {
            richTextBox4.Text = returnSpinnedContent(richTextBox3.Text);
        }