about being careful about these sorts of things," said Eric R. Robinson '01, a cognitive neuroscience concentrator who worked there last summer.

"Professor Hauser makes sure that people are cautious about letting people on the floor with the animals," he said.

On Friday evening, a security guard stopped a man wearing a tweed jacket from entering one of the William James lobby elevators. According to a police source, the man asked the security guard whether there was animal testing in the building.

The guard called police when the man denied that he was affiliated with the building.

Saturday night, the heavier police presence was visible. Students from an undergraduate group received permission to hold a party on the fifteenth floor, but a security guard, mishearing one of the students, notified HUPD dispatchers that the group was affiliated with animal rights protesters.

HUPD officers raced to the building, checked to make sure all the doors and windows were locked and continued a close patrol of the area.

Officials acknowledge the recent increase in attention paid to the lab has made them nervous.

Professor Daniel L. Schacter, chair of the psychology department, confirmed administrators had e-mailed department members and staff about the threats, though he declined to elaborate on the nature of what was advised.