Trading in the options of Cerevel Therapeutics Holdings Inc. (CERE.O) saw an unprecedented increase along with its stock price in the days leading up to the news made on Wednesday that AbbVie (ABBV.N) would purchase the drug developer in a transaction for multiple billions of dollars.

Following the close of the market on Wednesday, AbbVie announced that it will acquire Cerevel for around $8.7 billion to replace income as its trendy arthritis medication Humira confronts competition from a wide variety of new companies. Just a few minutes after Reuters reported that a deal was becoming close, the announcement was made.

The shares of Cerevel, which had already increased by 42% for the previous three trading sessions, increased by an additional 16% to reach a high of $42.75 in trading after the bell. The price of AbbVie’s offer was $45 per share.

An enormous increase in options activity followed the recent rise in stock prices throughout a few sessions. Both call-and-put options allow investors to purchase and sell shares at predetermined prices in the future. These options can be utilized as hedges or as a means of speculating on the fluctuations of share prices.

According to the data provided by Trade Alert, the number of contracts that have changed hands throughout the previous three sessions for Cerevel’s options was over 51,000. Before the current activity surge, their typical daily trading volume was less than 320 contracts.

According to Matt Amberson, a principal of the options analytics firm ORATS, “Something about this is completely suspicious.” “I’m almost certain that someone in the know is behind this.”

A request for comment made outside of regular business hours was not met with a response from the United States Securities and Exchange Commission (SEC). In addition, representatives from the Financial Industry Regulatory Authority did not immediately reply to a request for comment.

When a request for comment was made outside of regular business hours, neither Cerevel nor AbbVie responded to the inquiry.

On December 4, traders bought short-dated upside call options on Cerevel, which are contracts that would make money if the stock soared dramatically in a short period. This activity began with the stock and increased in tandem with stock trading.

The volume of Cerevel options increased to 6,500 contracts on December 4, and by the middle of January, almost 1,800 contracts were being traded. Call options betting on the stock had risen to more than $35 and were trading. The stock had finished the previous trading session at $26.

On December 4, the call options on the stock that had finished trading at more than $25 by the middle of the month were the second most frequently traded contracts.

“That’s unusual call activity for this stock,” said Brent Kochuba, the creator of SpotGamma, a startup that provides options analytics consulting.

“Some of this looks fishy; it does not look clean,” he said.

During the trading session on Wednesday, the most significant transactions in Cerevel options were spreads. Put spreads are a combination of December options that protect against a decline in the stock price below $35.

Los Angeles-based Capital Market Laboratories’ chief executive officer, Ophir Gottlieb, suggested that a trader may have made the trades to preserve recent stock price gains or hope that the price increase would prove to be transient. However, it was not clear what the motive behind the trade that occurred on Wednesday was.

Analysts believe that regulatory authorities will likely scrutinize the options deals due to the peculiar nature and timing of the trades.

There have been instances in which the activity of options has increased before the public announcement of agreements, and the Securities and Exchange Commission (SEC) has in the past announced enforcement action for alleged insider trading, including options trading.